全文获取类型
收费全文 | 4641篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 30篇 |
金属工艺 | 11篇 |
机械仪表 | 2篇 |
建筑科学 | 7篇 |
能源动力 | 1篇 |
轻工业 | 27篇 |
水利工程 | 2篇 |
无线电 | 5篇 |
一般工业技术 | 15篇 |
冶金工业 | 4521篇 |
原子能技术 | 2篇 |
自动化技术 | 20篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2013年 | 12篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 4篇 |
2007年 | 1篇 |
2006年 | 4篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 2篇 |
1999年 | 153篇 |
1998年 | 1361篇 |
1997年 | 739篇 |
1996年 | 510篇 |
1995年 | 265篇 |
1994年 | 237篇 |
1993年 | 256篇 |
1992年 | 36篇 |
1991年 | 73篇 |
1990年 | 60篇 |
1989年 | 85篇 |
1988年 | 72篇 |
1987年 | 64篇 |
1986年 | 70篇 |
1985年 | 55篇 |
1983年 | 5篇 |
1982年 | 16篇 |
1981年 | 28篇 |
1980年 | 48篇 |
1979年 | 3篇 |
1978年 | 10篇 |
1977年 | 121篇 |
1976年 | 268篇 |
1975年 | 5篇 |
1955年 | 3篇 |
1954年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有4647条查询结果,搜索用时 15 毫秒
141.
Y Cottin C Touzery F Dalloz B Coudert M Toubeau A Riedinger P Louis JE Wolf F Brunotte 《Canadian Metallurgical Quarterly》1998,21(9):665-670
This article reports on the effect of dietary modification on changes in eating patterns and serum lipids among hypercholesterolemic persons aged 40-59 years with no evidence of coronary heart disease in Mae Sot District, Tak Province, between 1995 and 1996. A total of 381 persons with total cholesterol levels > or = 240 mg/dl and triglyceride levels < 400 mg/dl were educated, counseled, and followed-up by the mobile health team at the health centres in the communities. The team comprised both hospital personnel (a physician, a health educator, and public health nurses) and the health centre workers. Of the 381 study persons, 331 (86.9%) completed the one-year follow-up. The participants at one-year follow-up were more likely than at baseline to reduce intakes of dietary fat and cholesterol, whereas, there was an increased intake of vegetables and fruits. The mean total cholesterol level significantly decreased from 258.9 mg/dl at baseline to 236.1 mg/dl at one-year follow-up (p < 0.01), giving an 8.8 per cent reduction. The mean change in low-density lipoprotein cholesterol levels was a 26.0 mg/dl decrease (p < 0.01), yielding a 15.1 per cent fall. The mean high-density lipoprotein cholesterol level increased from 44.6 mg/dl at baseline to 46.8 mg/dl at one-year follow-up (p < 0.01). The proportion of those who had a body mass index of < 25 slightly increased from 70.7 per cent at baseline to 72.5 per cent at one-year follow-up. The dietary intervention program by the mobile team may be useful for lowering serum cholesterol among the rural population with hypercholesterolemia. 相似文献
142.
143.
144.
PH Allaire JM Messick JE Oesterling DE Byer RP Myers MM Lieber RC Chantigian JO Welna DE Patterson ML Blute 《Canadian Metallurgical Quarterly》1992,67(11):1031-1041
In a prospective, randomized study, continuous infusion of epidural fentanyl citrate (group E) was compared with patient-controlled intravenously administered morphine sulfate (group P) for analgesia in 66 men after radical retropubic prostatectomy. Although both methods provided satisfactory analgesia, the mean comfort level scores were lower (that is, greater comfort) in group E than in group P at all observation times. The difference in mean resting comfort level scores between groups E and P was statistically significant (P < or = 0.05) at 9 of the 11 observation times. In addition, significant differences in comfort level scores were noted at 8 of the 11 observation times during deep breathing, 5 of 11 during coughing, and 3 of 9 during ambulation. Maximal and minimal comfort level scores recorded by each patient during the course of the study were significantly lower (that is, less pain) in group E than in group P for all four categories of activity. The percentage of patients who reported no pain was significantly higher in group E than in group P at 9 of 11 observation times during resting and 5 of 11 observation times during deep breathing. No significant differences were noted in side effect profiles or duration of hospital stay. In summary, when two effective methods of analgesia used after radical retropubic prostatectomy were compared prospectively, patients who received epidural infusion of fentanyl were more comfortable than those with patient-controlled intravenous administration of morphine, as evidenced by lower mean, maximal, and minimal comfort level scores and a greater proportion of patients with complete relief of pain. 相似文献
145.
146.
To investigate the developmental fates and the migratory pathways of dividing progenitors in both the white matter (WM) and the external granule layer (EGL) in the early postnatal rat cerebellum, a replication-deficient retrovirus carrying the beta-galactosidase gene (BAG) was injected into the deep cerebellar tissue or the EGL of postnatal rats to label dividing progenitors. After 1-3 days post-injection (1-3 dpi) of BAG into the deep cerebellar tissue of postnatal day 4/5 (P4/5) rats, labeled immature, unipolar cells were found mainly in the WM. From 4 to 6 dpi, similar cells appeared in the internal granule (IGL), Purkinje cell, and molecular layers, although about half of the labeled cells still resided in the WM and appeared immature. The first morphologically definable Bergmann glia, astrocytes, and oligodendrocytes were also observed. From 14 to 20 dpi, most labeled cells had developed into Bergmann glia, astrocytes, oligodendrocytes, and interneurons in their appropriate layers. When BAG injections were performed at P14, unipolar cells were initially observed, but the majority of these differentiated into myelinating oligodendrocytes in the WM and IGL by 17 dpi. Few immature cells were labeled by injections administered at P20, and these did not develop into mature glia, but into cells with lacy, fine processes, possible representing immature oligodendrocytes. In contrast, BAG-labeled progenitors of EGL produced only granule neurons. Thus, within the first 2 postnatal weeks, dividing progenitors in the WM migrate as immature cells into the cortex before differentiating into a variety of glia and interneurons. The genesis of oligodendrocytes continues through the 2nd postnatal week and largely ceases by P20. EGL cells do not produce glia, but only granule cells. 相似文献
147.
JD Meyer RF Falk RM Kelly JE Shively SJ Withrow WS Dernell DJ Kroll TW Randolph MC Manning 《Canadian Metallurgical Quarterly》1998,87(9):1149-1154
A new method for preparing poly(L-lactide) (PLA) biodegradable beads impregnated with an ionic aminoglycoside, gentamycin, is described. The process employs hydrophobic ion pairing to solubilize gentamycin in a solvent compatible with PLA, followed by precipitation with a compressed antisolvent (supercritical carbon dioxide). The resulting precipitate is a homogeneous dispersion of the ion-paired drug in PLA microspheres. The microspheres are approximately 1 microm in diameter and can be compressed into beads (3-6 mm in diameter) strung on surgical sutures for implantation. The bead strings exhibit no significant change in release kinetics upon sterilization with a hydrogen peroxide plasma (Ster-Rad). The kinetics of gentamycin release from the PLA beads are consistent with a matrix-controlled diffusion mechanism. While nonbiodegradable poly(methyl methacrylate) (PMMA) beads initially release gentamycin in a similar manner, the drug release from PMMA ceases after 8 or 9 weeks, while the PLA beads continue to release drug for over 4 months. Moreover, only 10% of the gentamycin is released from the PMMA beads, while PLA beads release more than 60% of their load, if serum is present in the release medium. The PLA system displays improved release kinetics relative to PMMA, is biodegradable, is unaltered by gas sterilization, can be used for a range of antibiotics, and can be manipulated without disintegration. These are all desirable properties for an implantable drug delivery system for the prevention or treatment of osteomyelitis. 相似文献
148.
Vascular endothelial cells are linked by gap junctions, which facilitate the propagation of electrical and chemical signals along the vessel wall. The aim of this study was to determine the distribution and identity of the gap junction structural proteins (connexins) expressed by endothelial cells in situ. Connexin expression in different regions of the rat aortic endothelium was analyzed with the use of indirect immunofluorescence microscopy and Western blotting. Connexin40 and connexin37 were present in most, if not all, of the thoracic and abdominal aortic endothelia in the form of maculae at cell-cell appositions. In contrast, connexin43 was undetectable in most endothelia but extremely abundant in small numbers of cells localized at the downstream edge of the ostia of branching vessels and at flow dividers, regions that experience turbulent shear stress from disturbed blood flow. To examine the relationship of shear stress and connexin43 expression, localized stress was induced by surgical coarctation of the aorta, which was sufficient to cause striking local upregulation of connexin43 within 8 days. Thus, increases in connexin43 levels are an endothelial response to mechanical stress. 相似文献
149.
1. Age-matched (3-4 months old) male, heterozygous, hypertensive, transgenic ((mRen-2)27) rats (abbreviated to TG rats) and the normotensive control animals (homozygous, Hannover Sprague-Dawley rats (abbreviated to SD rats), were chronically instrumented for the assessment of regional haemodynamic responses to continuous lipopolysaccharide (LPS) infusion (150 microg kg(-1) h(-1), i.v.) 2. The early (1-2 h) hypotension in SD rats (-11+/-3 mmHg; n=7) was significantly less than that in TG rats (-35+/-3 mmHg; n=8), but by 24 h mean arterial blood pressure (MAP) in both strains of rat was not different from the pre-LPS value (SD rats: baseline, 108+/-3 mmHg; 24 h LPS, 112+/-4 mmHg; TG rats: baseline, 171+/-2 mmHg; 24 h LPS, 169+/-3 mmHg). At this stage in the SD rats there was a renal vasodilatation (delta vascular conductance, 29+/-10 [kHz mmHg(-1)]10(3)) but not in TG rats (delta vascular conductance 2+/-3[kHz mmHg(-1)]10(3)). 3. Co-infusion of LPS and the non-selective endothelin receptor antagonist, SB 209670 (600 microg kg(-1) bolus, 600 microg kg(-1) h(-1)) between 24 and 31 h in SD rats caused a fall in MAP of 16+/-2 mmHg accompanied by hindquarters vasodilatation (delta vascular conductance 11+/-3 (kHz mmHg(-1))10(3)). In TG rats, under the same conditions, the fall in MAP was -60+/-6 mmHg, and there were renal, mesenteric and hindquarters vasodilatations (delta vascular conductance, 23+/-5, 32+/-7, and 14+/-4 (kHz mmHg(-1))10(3), respectively). All effects, except the hindquarters vasodilatation, were greater in TG than in SD rats. 4. In TG rats infused with LPS alone for 31 h, between 24 and 31 h the fall in MAP was -17+/-4 mmHg, and the changes in renal, mesenteric and hindquarters vascular conductances were 5+/-3, -4+/-5, and 12+/-4 (kHz mmHg(-1)10(3), respectively. 5. Administration of the angiotensin (AT1)-receptor antagonist, losartan (10 mg kg(-1), i.v.) following co-infusion of LPS and SB 209670 between 24 and 31 h caused similar falls in MAP in SD and TG rats (-12+/-3 and -14+/-4 mmHg, respectively). 6. These results, together with previous findings, are consistent with a relative enhancement of the contribution of endothelin to the maintenance of cardiovascular status in endotoxaemic TG rats, particularly through a mesenteric vasoconstrictor action. 相似文献
150.
The rice blast fungus, Magnaporthe grisea, generates enormous turgor pressure within a specialized cell called the appressorium to breach the surface of host plant cells. Here, we show that a mitogen-activated protein kinase, Mps1, is essential for appressorium penetration. Mps1 is 85% similar to yeast Slt2 mitogen-activated protein kinase and can rescue the thermosensitive growth of slt2 null mutants. The mps1-1Delta mutants of M. grisea have some phenotypes in common with slt2 mutants of yeast, including sensitivity to cell-wall-digesting enzymes, but display additional phenotypes, including reduced sporulation and fertility. Interestingly, mps1-1Delta mutants are completely nonpathogenic because of the inability of appressoria to penetrate plant cell surfaces, suggesting that penetration requires remodeling of the appressorium wall through an Mps1-dependent signaling pathway. Although mps1-1Delta mutants are unable to cause disease, they are able to trigger early plant-cell defense responses, including the accumulation of autofluorescent compounds and the rearrangement of the actin cytoskeleton. We conclude that MPS1 is essential for pathogen penetration; however, penetration is not required for induction of some plant defense responses. 相似文献