全文获取类型
收费全文 | 2054篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
综合类 | 6篇 |
化学工业 | 38篇 |
金属工艺 | 6篇 |
机械仪表 | 8篇 |
建筑科学 | 6篇 |
轻工业 | 17篇 |
水利工程 | 5篇 |
石油天然气 | 3篇 |
无线电 | 20篇 |
一般工业技术 | 24篇 |
冶金工业 | 1843篇 |
自动化技术 | 91篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 5篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 1篇 |
2009年 | 6篇 |
2008年 | 6篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 57篇 |
1998年 | 628篇 |
1997年 | 347篇 |
1996年 | 192篇 |
1995年 | 132篇 |
1994年 | 104篇 |
1993年 | 113篇 |
1992年 | 19篇 |
1991年 | 35篇 |
1990年 | 30篇 |
1989年 | 33篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 13篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 22篇 |
1976年 | 73篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2067条查询结果,搜索用时 15 毫秒
991.
JV O'Doherty CS Nolan PC McCarthy 《Journal of the science of food and agriculture》2005,85(3):371-380
In experiment 1, 224 pigs (initially 8.85 kg and 28 ± 2 days of age) were used in a 2 × 2 factorial arrangement of treatments to investigate the interaction between lactofeed (LF70) (860 g kg?1 whey permeate, 140 g kg?1 soya bean meal) level (175 g kg?1 and 350 g kg?1) and avilamycin (0 and 40 mg kg?1) inclusion in piglet starter diets. Pigs were fed starter diets from day 0 to day 22 and a transition diet was fed from day 23 to day 39. The inclusion level of LF70 in the transition diet was 75 g kg?1 and 150 g kg?1. Pigs fed 350 g kg?1 LF70 had a higher daily gain (ADG) (p < 0.01) and an improved feed conversion ratio (FCR) (p < 0.05) during the starter period than the pigs fed 175 g kg?1 LF70. Pigs fed medicated diets had a higher ADG (p < 0.05) and an improved FCR (p < 0.05) than the non‐medicated fed pigs during the starter period. There was an increase in feed intake (AFI) (p < 0.05) during the transition period with increasing levels of LF70. There was an improvement in FCR during the transition period with the inclusion of avilamycin (p < 0.01). There was a significant interaction (p < 0.01) between LF70 and avilamycin for ADG during the transition period. The inclusion of avilamycin at 175 g kg?1 LF70 inclusion had no effect (p > 0.05) on ADG. However at 350 g kg?1 LF70 inclusion the pigs offered medicated diets had a higher ADG (p < 0.001) compared with non‐medicated diets. In experiment 2, 224 pigs (initially 8.85 kg and 28 ± 2 days of age) were used in a 2 × 2 factorial to investigate the interaction between LF70 level (175 g kg?1 and 350 g kg?1) and zinc oxide (ZnO) (0 and 3.1 g kg?1) inclusion in piglet starter diets. The inclusion level of LF70 in the transition diet was 75 g kg?1 and 150 g kg?1 and of ZnO was 2 g kg?1. There was a significant increase (p < 0.05) in ADG with increasing levels of LF70 during the starter period. The inclusion of ZnO during the starter period resulted in an increase in ADG (p < 0.001) and FCR (p < 0.05) compared with no ZnO inclusion. Neither the inclusion of zinc oxide not of LF70 had an effect (p > 0.05) on performance during the transition period. In conclusion the supplementation of starter diets with increasing levels of LF70, ZnO and avilamycin resulted in increased ADG and improved FCR. Copyright © 2004 Society of Chemical Industry 相似文献
992.
Small quantities of botulinum toxin (BTX) are useful in the treatment of certain movement disorders, such as laryngeal spasmodic dysphonia, blepharospasm, and cervical dystonia. However, the corrective paralytic effects of BTX are only temporary, in part because of the formation of remodeled neuromuscular junctions. Here, we questioned whether various factors within and near the neuromuscular junction could contribute to the remodeling seen after BTX treatment. BTX was injected subcutaneously in the region of the levator auris longus muscle. At 1-week intervals, levator auris longus muscles were removed and examined histochemically. As previously described, BTX treatment results in a progressive elongation of end plates. The neural cell adhesion molecule was not associated with the elongated end plates but was associated with the BTX-induced nerve sprouts after long intervals (3 to 4 weeks). Similarly, after BTX, laminin-1 (composed of alpha 1, beta 1, and gamma 1 chains) reactivity was associated with the nerve sprouts, but not with the end plates. Laminin beta 2 reactivity at the end plate dispersed somewhat within 1 week but remained diffusely associated with the elongating end plates for up to 5 weeks. Together these results suggest that neural cell adhesion molecule and laminins may participate in the sprouting observed after BTX treatment and that alterations in laminin beta 2 expression may participate in initial loss of contacts. 相似文献
993.
OBJECTIVE: To compare the pharmacology, pharmacokinetics, and efficacy of the newer atypical antipsychotics with those of conventional agents and existing atypical agents. DATA SOURCES: Information was retrieved from a MEDLINE English-literature search from July 1986 to June 1998 and by review of references. Indexing terms included neuroleptics, atypical antipsychotics, clozapine, risperidone, olanzapine, sertindole, quetiapine, and ziprasidone. STUDY SELECTION: Comparative studies were selected when possible; placebo-controlled studies were included when data were limited on newer atypical antipsychotics. DATA EXTRACTION: Emphasis was placed on properly designed clinical trials that assessed dosage, expanded efficacy, enhanced adverse effect profile, and cost. DATA SYNTHESIS: Like other atypical antipsychotics, the newer agents have an enhanced 5-hydroxytryptophan/dopaminergic receptors (5-HT2/D2) affinity ratio and undergo extensive biotransformation. Risperidone and olanzapine demonstrate more favorable efficacy/adverse effect ratios than clozapine, sertindole, and conventional antipsychotics in nonrefractory and refractory schizophrenics. Future studies will more clearly define the role of quetiapine and ziprasidone in antipsychotic therapy. CONCLUSIONS: Data from controlled trials on efficacy and extrapyramidal side effects support risperidone or olanzapine as first-line agents for the treatment of schizophrenia. Pharmacologic and pharmacokinetic factors do not distinguish between agents sufficiently for drug selection. 相似文献
994.
RW Light MJ Peng DW Stansbury CS Sassoon JA Despars CK Mahutte 《Canadian Metallurgical Quarterly》1999,115(1):102-108
Granulocyte-macrophage colony-stimulating factor (GM-CSF)-transduced B16-F10 murine melanoma cells had lower tumorigenicity in both syngeneic and nude mice than parental or LacZ-transduced (control) cells. The subcutaneous (s.c.) tumors producing GM-CSF were densely infiltrated with macrophages, whereas the control tumors were not. In vitro studies showed that GM-CSF-transduced B16 cells were susceptible to lysis mediated by nonactivated murine macrophages, whereas control B16 cells were not. Macrophage-mediated cytotoxicity against GM-CSF-transduced B16 cells was independent of the presence of NO, H2O2, O2-, tumor necrosis factor alpha, and matrix metalloproteinase. Coculture experiments using GM-CSF-producing and -nonproducing B16 cells demonstrated that GM-CSF produced by the transduced B16 cells activated macrophages to kill the bystander non-GM-CSF-producing tumor cells. The results suggest that GM-CSF released by tumor cells can induce macrophage-mediated cytotoxicity, which in turn can inhibit the in vivo growth of GM-CSF-transduced tumor cells. 相似文献
995.
JR Milanez de Campos CS Barbas LT Filomeno A Fernandez H Minamoto JV Filho FB Jatene 《Canadian Metallurgical Quarterly》1997,112(3):729-733
The involvement of phosphatidylinositol 3-kinase (PI3K) in the induction of ornithine decarboxylase (ODC) was investigated by using specific PI3K inhibitors. In difluoromethylornithine-resistant L1210 cells stimulated to growth from quiescence, treatment with LY294002 inhibited cell growth and provoked a complete block of the induction of ODC activity (IC50 approximately 2 microM) and ODC protein. Some reduction in the accumulation of ODC mRNA was also observed, whereas ODC turnover was not affected significantly. Wortmannin, another specific inhibitor of PI3K, structurally unrelated to LY294002, also inhibited ODC induction with an IC50 of about 10 nM. These results indicate that PI3K activity is required for the induction of ODC, possibly affecting both ODC mRNA level and translation. Since p70 S6 kinase (p70S6K) is considered an important mediator of PI3K action in several experimental systems, the effect of rapamycin, which can lead to selective inhibition of p70S6K, was also investigated. Rapamycin inhibited p70S6K activity and produced ODC inhibiting effects similar to those elicited by LY294002. However, LY294002 and wortmannin at concentrations which inhibited almost completely PI3K activity did not decrease p70S6K activity, suggesting that p70S6K does not mediate the PI3K effects on ODC, but may lie on a separate pathway in this experimental model. 相似文献
996.
A Pollack CS Wu B Czerniak GK Zagars WF Benedict TJ McDonnell 《Canadian Metallurgical Quarterly》1997,3(10):1823-1829
The objective of this study was to determine whether the overexpression of bcl-2, a key protein governing the apoptotic response to radiation, adds to pRb status in estimating the propensity for radiation response in patients with muscle-invasive bladder cancer. Archival formalin-fixed, paraffin-embedded, pretreatment bladder tumor samples were available in 109 of 301 patients treated preoperatively with 50 Gy in 25 fractions followed by radical cystectomy 4-6 weeks later. Radiation response was assessed by clinical-to-pathological tumor downstaging or upstaging. Altered expression of bcl-2 (47% of 107 patients), p53 (56% of 109 patients), and pRb (30% of 98 patients) was assessed by immunohistochemical staining. Morphological criteria were used to calculate the percentage of apoptotic cells. bcl-2 staining correlated with tumor grade; all grade 2 tumors (n = 7) displayed normal bcl-2 expression (negative staining). No correlations between bcl-2 staining and pretreatment apoptosis levels, p53 staining, and pRb staining were observed. In terms of the radiation response parameters, univariate analyses revealed that bcl-2 overexpression was the only factor associated with upstaging. The main predictor of downstaging was the loss of pRb expression (negative staining). Multivariate logistic regression confirmed these findings and also showed that normal pRb expression (positive staining) was significantly related to upstaging. Patient outcome was adversely affected by bcl-2 overexpression, because these patients experienced significantly increased actuarial local failure rates. No difference in distant metastasis or survival rates by bcl-2 staining was seen. The strongest independent correlates of radiation response thus far identified in muscle-invasive bladder cancer are from bcl-2 and pRb immunohistochemical staining. The overexpression of bcl-2 and the normal expression of pRb seem to thwart the apoptotic response to radiation via independent mechanisms. Abnormalities in the expression of proteins that regulate apoptosis may prove to establish a molecular phenotype to characterize which patients should receive radiotherapy. 相似文献
997.
Classical A kinase anchor proteins (AKAPs) preferentially tether type II protein kinase A (PKAII) isoforms to sites in the cytoskeleton and organelles. It is not known if distinct proteins selectively sequester regulatory (R) subunits of type I PKAs, thereby diversifying functions of these critical enzymes. In Caenorhabditis elegans, a single type I PKA mediates all aspects of cAMP signaling. We have discovered a cDNA that encodes a binding protein (AKAPCE) for the regulatory subunit (RCE) of C. elegans PKAICE. AKAPCE is a novel, highly acidic RING finger protein composed of 1,280 amino acids. It binds RI-like RCE with high affinity and neither RIIalpha nor RIIbeta competitively inhibits formation of AKAPCE.RCE complexes. The RCE-binding site was mapped to a segment of 20 amino acids in an N-terminal region of AKAPCE. Several hydrophobic residues in the binding site align with essential Leu and Ile residues in the RII-selective tethering domain of prototypic mammalian AKAPs. However, the RCE-binding region in AKAPCE diverges sharply from consensus RII-binding sites by inclusion of three aromatic amino acids, exclusion of a highly conserved Leu or Ile at position 8 and replacement of C-terminal hydrophobic amino acids with basic residues. AKAPCE.RCE complexes accumulate in intact cells. 相似文献
998.
BACKGROUND: Despite current recommendations of flexible sigmoidoscopy as a screening test for the detection of colorectal carcinoma, relatively few asymptomatic patients undergo this procedure. To enhance the use of sigmoidoscopy, differences in the use of screening, as well as barriers to screening among specific physician groups, should be defined. METHODS: The authors surveyed 1762 practicing primary care physicians to determine their self-reported ability to perform sigmoidoscopy and perceived obstacles to either initiating or enhancing screening. RESULTS: A total of 884 physicians (50%) responded. Ninety percent of primary care physicians reported that they offered sigmoidoscopic screening to their patients, with 46% referring patients and 44% performing the procedure themselves. Physician characteristics were not associated with the overall use of sigmoidoscopy. In contrast, compared with physicians who referred patients for the procedure, physicians who performed sigmoidoscopy themselves were more often board certified, male, and graduated from medical school after 1970 (P < 0.001). In a multivariate analysis, these characteristics were also independently associated with the ability to perform sigmoidoscopy. The barrier to sigmoidoscopy cited most often was poor patient acceptance, whether or not the physician performed or referred patients for sigmoidoscopic screening. Other barriers cited were lack of training, lack of equipment, and time required, each of which was identified most often by physicians who did not screen at all. CONCLUSIONS: Most physicians surveyed reported using sigmoidoscopic screening to some degree in their practice, although many did not perform the procedure themselves. Population-based interventions to increase screening may benefit from targeting specific physician subgroups and attempting to improve patient acceptance of the procedure. 相似文献
999.
Phosphopeptides are a useful tool for the investigation of phosphorylation as a reversible posttranslational modification. There is a growing interest in using mimics of phosphoamino acids involved in phosphorylation in order to study the enzymes concerned in these processes. These mimics should contain a non-hydrolysable or isoelectrically modified phosphate moiety to be used as a specific inhibitor of phosphatases and kinases. We introduce sold-phase synthesis of H- and methylphosphonopeptides as a new class of mimics of phosphotyrosyl peptides. The peptides were synthesized on solid phase using the standard fluorenyl-methyloxycarbonyl (Fmoc) strategy. Tyrosine residues were incorporated as allyl-protected derivatives, which were selectively deprotected on the resin by treatment with Pd(PPh3)4. The peptide resin carrying the side-chain unprotected tyrosine of the model peptide Gly-Gly-Tyr-Ala was phosphonylated with di-tert-butyl-N,N-diethyl-phosphoramidite in the presence of 1H-tetrazole, yielding H-phosphonopeptides after trifluoroacetic acid (TFA) cleavage. Alternatively, phosphonylation of the unprotected tyrosine with O-tert-butyl-N,N-diethyl-P-methylphosphonamidite catalysed by 1H-tetrazole and followed by oxidation led to the methyphosphonopeptides after TFA cleavage. We obtained both the H-phosphonopeptides and the methylphosphonopeptides of the tetrapeptide in high yields and purities above 90%, according to reversed-phase high-performance liquid chromatography (RP-HPLC). To investigate the general applicability of our new methodology, we synthesized phosphonopeptides up to 13 amino acids long, corresponding to recognition sequences of tyrosine kinases. After cleavage and deprotection, all phosphonopeptides were obtained in high yields and purities of about 90%, as shown by mass spectrometry. The only by-product found was the unmodified peptide. 相似文献
1000.
H Shinotoh BJ Snow NS Chu CC Huang CS Lu C Lee H Takahashi DB Calne 《Canadian Metallurgical Quarterly》1997,48(4):1053-1056
We performed PET on four patients with chronic industrial Mn intoxication; presynaptic and postsynaptic dopaminergic function were measured with [18F]6-fluoro-L-dopa (6FD) and [11C]raclopride (RAC). All patients had a rigid-akinetic syndrome; they had no sustained benefit from L-dopa. Influx constants (Ki) of 6FD were normal in the caudate and putamen. RAC binding was mildly reduced in the caudate and normal in the putamen. We conclude that nigrostriatal dopaminergic dysfunction is not responsible for the parkinsonism caused by chronic Mn intoxication. The pathology is likely to be downstream of the dopaminergic projection. 相似文献