全文获取类型
收费全文 | 4322篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 44篇 |
综合类 | 2篇 |
化学工业 | 402篇 |
金属工艺 | 82篇 |
机械仪表 | 168篇 |
建筑科学 | 56篇 |
矿业工程 | 3篇 |
能源动力 | 112篇 |
轻工业 | 83篇 |
水利工程 | 26篇 |
石油天然气 | 8篇 |
无线电 | 511篇 |
一般工业技术 | 485篇 |
冶金工业 | 1860篇 |
原子能技术 | 19篇 |
自动化技术 | 525篇 |
出版年
2023年 | 26篇 |
2022年 | 57篇 |
2021年 | 57篇 |
2020年 | 50篇 |
2019年 | 53篇 |
2018年 | 66篇 |
2017年 | 57篇 |
2016年 | 81篇 |
2015年 | 54篇 |
2014年 | 65篇 |
2013年 | 171篇 |
2012年 | 88篇 |
2011年 | 129篇 |
2010年 | 106篇 |
2009年 | 99篇 |
2008年 | 102篇 |
2007年 | 96篇 |
2006年 | 90篇 |
2005年 | 80篇 |
2004年 | 59篇 |
2003年 | 60篇 |
2002年 | 66篇 |
2001年 | 55篇 |
2000年 | 63篇 |
1999年 | 107篇 |
1998年 | 632篇 |
1997年 | 344篇 |
1996年 | 255篇 |
1995年 | 139篇 |
1994年 | 125篇 |
1993年 | 155篇 |
1992年 | 60篇 |
1991年 | 54篇 |
1990年 | 54篇 |
1989年 | 52篇 |
1988年 | 48篇 |
1987年 | 40篇 |
1986年 | 40篇 |
1985年 | 46篇 |
1984年 | 23篇 |
1983年 | 34篇 |
1982年 | 36篇 |
1981年 | 37篇 |
1980年 | 36篇 |
1979年 | 34篇 |
1978年 | 17篇 |
1977年 | 53篇 |
1976年 | 74篇 |
1975年 | 14篇 |
1973年 | 11篇 |
排序方式: 共有4386条查询结果,搜索用时 15 毫秒
911.
912.
Helicobacter pylori lipopolysaccharide (LPS) expresses Lewis x and Lewis y blood group antigens that are identical to those occurring in the human gastric mucosa. During infection, antibodies against LPS, which bind to host Lewis antigens, may be induced. These consequently recognize gastric glycoprotein targets and cause autoimmune inflammation. 相似文献
913.
914.
TV Cacciarelli M Green R Jaffe GV Mazariegos A Jain JJ Fung J Reyes 《Canadian Metallurgical Quarterly》1998,66(8):1047-1052
BACKGROUND: Posttransplant lymphoproliferative disease (PTLD) after pediatric liver transplantation has been associated with high mortality rates. METHODS: The present study examined 282 consecutive pediatric liver transplant recipients from October 1989 to June 1996 who received primary tacrolimus immunosuppression. The aim was to determine the incidence of PTLD, management strategies, and patient outcome. RESULTS: The incidence of PTLD was 13% (361282) with a mean age of 5.5+/-0.7 years (range 0.6 to 15) at diagnosis. The average time from transplantation to PTLD was 10.1+/-2.1 months. Initial treatment of PTLD consisted of reduction (3 patients) or discontinuation (33 patients) of tacrolimus and initiation of antiviral therapy (intravenous ganciclovir, 14 patients; intravenous acyclovir, 22 patients; or both, 5 patients). Alpha-interferon was used in four patients (two successfully). One patient also received gamma-interferon, chemotherapy, and radiation for a central nervous system lesion. Chemotherapy was also used in one patient with Burkitt's, whereas one patient with a pulmonary lesion received additional radiation therapy. Three patients received supportive surgery for gastrointestinal involvement, and one patient had a splenectomy for hemolysis. Overall mortality was 22% (8/36) with 5 (14%) PTLD-related deaths (disseminated disease, 4 patients; bowel perforation, 1 patient). Of 31 survivors, 23 had acute rejection at a median time of 24 days after PTLD, with 2 patients developing chronic rejection. One patient required retransplantation. Present immunosuppression consists of tacrolimus monotherapy in 14 patients, tacrolimus/prednisone in 8 patients, and none in 6 patients. CONCLUSION: In summary, PTLD can be successfully treated with reduction of immunosuppression and administration of antiviral agents in most patients. The management of rejection after PTLD requires reassessment of disease status and judicious reintroduction of immunosuppression therapy. 相似文献
915.
916.
S Nakata S Honma K Numata K Kogawa S Ukae N Adachi X Jiang MK Estes Z Gatheru PM Tukei S Chiba 《Canadian Metallurgical Quarterly》1998,36(11):3160-3163
An epidemiological survey on human calicivirus (HuCV) infections and associated gastroenteritis in infants was conducted to clarify the prevalence of HuCV infections in infants and adults in Kenya. Enzyme immunoassays (EIAs) for three genogroups of HuCVs, Norwalk virus (NV), Mexico virus (MXV), and Sapporo virus (SV), were used to detect antigen or antibody. We tested 1,431 stool samples obtained from children younger than 6 years old with acute gastroenteritis who visited outpatient clinics in three districts in Kenya from August 1991 to July 1994. Thirty-two (2.2%) of these stool samples were positive for SV antigen. Only one (0.1%) of 1,186 samples was positive for NV antigen and none of 246 samples was positive for MXV antigen. One hundred ninety-three serum samples were tested for antibodies to NV and MXV, and 64 of them were examined for antibody to SV. The pattern of the age-related prevalence of serum antibody to NV was different from that of antibodies to MXV and SV. The acquisition of serum antibodies to HuCVs in the three genogroups appeared in early childhood, at about 1 to 2 years of age. The prevalence of serum antibody to NV was low (about 60%) throughout adulthood compared with a high prevalence of antibody (approximately 80 to 90%) to MXV and SV. These data indicate that infections with viruses in the three genogroups of HuCVs are common in Kenya, and immunological responses to NV may be different from those to MXV and SV. The EIAs for the detection of NV and MXV antigens appear to be quite specific for prototype NV and MXV strains, respectively, so that they can detect only a few strains of HuCVs related to them. Alternatively, NV and MXV caused less severe infections that did not bring children to the outpatient clinics for gastroenteritis in Kenya. 相似文献
917.
918.
RK Jain CF Piskorz BG Huang RD Locke HL Han A Koenig A Varki KL Matta 《Canadian Metallurgical Quarterly》1998,8(7):707-717
The selectins interact in important normal and pathological situations with certain sialylated, fucosylated glycoconjugate ligands containing sialyl Lewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has gone into the synthesis of sialylated and sulfated Lewisxanalogs as competitive ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and PSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure, we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1++ +-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for L and P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studies have shown that sulfate esters can replace sialic acid in some selectin ligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. , Nature, 361, 555, 1993). Based upon these observations, we hypothesized that Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability of interacting with L- and P-selectin. To examine this hypothesis, we synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2++ +-3Galbeta1-3)-GalNAc alpha1-OB, which was found to be 2- to 3-fold better than sialyl Lexfor P and L selectin, respectively. We also report the synthesis of an unusual structure GalNAcbeta1-4(Fucalpha1- 3)GlcNAcbeta1-OMe (GalNAc-Lewisx-O-methyl glycoside), which also proved to be a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe. Combining this with our knowledge of Core 2 branched structures, we have synthesized a molecule that is 5- to 6-fold better at inhibiting L- and P-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures, substitution of a sulfate ester group for a sialic acid residue in such a molecule resulted in a considerable loss of inhibition ability. Thus, the combination of a sialic acid residue on the primary (beta1-3) arm, and a modified Lexunit on the branched (beta1-6) arm on an O-linked Core 2 structure generated a monovalent synthetic oliogosaccharide inhibitor superior to SLexfor both L- and P-selectin. 相似文献
919.
Specific antibodies against structural proteins (actin, desmin, dystrophin, fibronectin) of muscle fibres were used to study the effect of forced lengthening contractions on muscle microarchitecture. Tibialis anterior (TA) muscle of male Wistar rats were subjected to 240 forced lengthening contractions. At consecutive time points (0, and 6 h, 2, 4, and 7 days) after stimulation, the TA muscle was excised for biochemical and histological assays. Beta-Glucuronidase activity, a quantitative indicator of muscle damage, showed increased values 2-7 days after the lengthening, peaking on day 4 (11.7-fold increase). A typical course of histopathological changes (myofibre swelling, necrosis and regeneration) was observed. In immunohistochemistry, the earliest abnormality observed was discontinuous dystrophin staining in some swollen fibres immediately after commencement of exercise, while at the same time no alterations occurred in the staining of the other antibodies studied. Six hours later, all the swollen fibres were uniformly desmin as well as dystrophin negative. The great majority, but not all, of the swollen fibres showed disorganized actin staining and intramyocellular localization of fibronectin. The early phase disruption of myofibre structures as measured in this study provides evidence of their central role following damage in skeletal muscle. These results suggest that the sequence of structural changes in the route to muscle fibre necrosis in injury induced by forced lengthening contraction originates in the disruption of the plasma membrane and the intermediate filament, which leads to disturbances in the myofibrillar system. 相似文献
920.
FF Ungacta VG Dávila-Román MJ Moulton BP Cupps P Moustakidis DS Fishman R Actis BA Szabo D Li NT Kouchoukos MK Pasque 《Canadian Metallurgical Quarterly》1998,65(4):943-950
We examined the relation between language dominance and regional cerebral blood flow (rCBF) during the intracarotid amobarbital procedure (IAP). A previous report limited to three patients suggested that dominant rather than nondominant hemisphere IAP may have a differential effect on rCBF. Behavioral assessment during the IAP also suggests that dominant hemisphere injection results in a differential effect on memory and affective symptoms rather than nondominant injection. Thirteen patients were assessed using single-photon emission CT (SPECT) brain imaging during both left and right IAP. The SPECTs were coregistered with the individual's MRI. Changes in rCBF during each IAP were compared with the patient's baseline SPECT. Nine patients had left hemisphere dominance, two were right dominant, and two had bilateral speech representation. In the left dominant subjects, left-hemisphere injection had a consistently greater effect on rCBF than right-hemisphere injection in the anterior (p < 0.005) and posterior (p < 0.01) temporal neocortex. There was also a trend for greater hypoperfusion in the frontal lobe of the left hemisphere. rCBF in the ipsilateral hippocampus was not significantly different after each injection (p > 0.05). In the two patients with right hemisphere speech, the reverse pattern was seen, with greater hypoperfusion after right (dominant) hemisphere injection. There was no consistent asymmetry in the two patients with bilateral speech. Dominant hemisphere IAP results in significantly greater hypoperfusion than does nondominant injection. These data provide a physiologic basis for behavioral differences noted after dominant versus nondominant IAP. 相似文献