首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2239篇
  免费   7篇
  国内免费   1篇
电工技术   12篇
化学工业   133篇
金属工艺   7篇
机械仪表   17篇
建筑科学   17篇
矿业工程   1篇
能源动力   11篇
轻工业   50篇
水利工程   1篇
石油天然气   1篇
无线电   60篇
一般工业技术   187篇
冶金工业   1685篇
原子能技术   2篇
自动化技术   63篇
  2021年   5篇
  2019年   6篇
  2017年   4篇
  2015年   5篇
  2014年   5篇
  2013年   26篇
  2012年   19篇
  2011年   20篇
  2010年   14篇
  2009年   15篇
  2008年   18篇
  2007年   15篇
  2006年   17篇
  2005年   9篇
  2004年   14篇
  2003年   23篇
  2002年   10篇
  2001年   5篇
  2000年   18篇
  1999年   68篇
  1998年   599篇
  1997年   324篇
  1996年   182篇
  1995年   114篇
  1994年   82篇
  1993年   133篇
  1992年   29篇
  1991年   27篇
  1990年   30篇
  1989年   26篇
  1988年   32篇
  1987年   26篇
  1986年   30篇
  1985年   27篇
  1984年   14篇
  1983年   18篇
  1982年   13篇
  1981年   19篇
  1980年   25篇
  1979年   15篇
  1978年   17篇
  1977年   34篇
  1976年   65篇
  1975年   8篇
  1974年   4篇
  1973年   5篇
  1972年   4篇
  1970年   4篇
  1969年   5篇
  1967年   3篇
排序方式: 共有2247条查询结果,搜索用时 15 毫秒
991.
Presents an obituary for Delos Wickens, a true generalist who, throughout his career, explored a wide range of areas including classical conditioning theory, human verbal learning, and human and animal memory. In addition to three textbooks, Wick authored or coauthored more than 100 experimental or theoretical articles. He served as associate editor for the Journal of Experimental Psychology, as well as ad hoc reviewer for several other journals and reviewer for several publishing houses. For many years he was a consultant for the National Science Foundation (NSF) and National Institute of Mental Health (NIMH). Wickens received a number of honors and awards, including the American Psychological Foundation's Distinguished Teaching Award, the highly prestigious Warren Medal from the Society of Experimental Psychologists, a Distinguished Alumni Award from the University of North Carolina, and a Distinguished Research Award from Ohio State University. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
993.
Direct injection of plasmid DNA into the myocardium of several species has been shown to be useful for studying cardiac gene expression. However, despite a better understanding of mouse genetics and the availability of several disease models in mice, gene injection with plasmid DNA into the mouse heart has not been reported. In this study, we demonstrate a simple and reproducible method for gene transfer into the mouse heart via direct injection of plasmid DNA. A firefly luciferase gene, driven by the RSV promoter, was used to quantitatively determine the spatial and temporal characteristics of gene transfer. Luciferase gene expression was stable for 8 weeks and showed a dose-dependent response over a range of 0.3-3 micrograms of input DNA. Inter-animal variability was low and gene expression was restricted to the left ventricle, near the site of injection. This method was also demonstrated to be suitable for detecting the expression of structural genes under the control of cellular promoters. Immunohistochemistry was used to detect the expression of an epitope-tagged myosin heavy chain driven by a rat alpha-myosin heavy chain promoter. Thus, naked DNA injection into the mouse heart results in a highly reproducible expression of constructs with either viral or cellular promoters. It is a relatively inexpensive and efficient means of studying cardiac gene regulation in vivo and a useful tool for screening the potential transgenes before generating transgenic mice.  相似文献   
994.
Genomic DNA fingerprint analysis was performed on 39 Staphylococcus aureus and 28 Enterococcus faecalis endophthalmitis isolates collected from multiple clinical centers. Among 21 S. aureus genomic DNA fingerprint patterns identified, five clonotypes were recovered from multiple unrelated patients and accounted for 58.9% (23 of 39) of the isolates analyzed. Compared with strains having unique genomic DNA fingerprint patterns, the S. aureus clonotypes occurring more than once were more likely to result in visual acuities of 20/200 or worse (P = 0.036 [chi2 test]). In contrast to the S. aureus isolates, the E. faecalis endophthalmitis isolates were a clonally diverse population, enriched for the expression of a known toxin, cytolysin, which is plasmid encoded.  相似文献   
995.
The contributions of the conceptus (embryo and associated membranes) and of the maternal endocrine milieu to control of endometrial secretory leukocyte protease inhibitor (SLPI, also designated antileukoproteinase) expression during the periimplantation stages of embryo development were examined in the present study. Uterine endometrium from distinct sites was collected from pigs at Days 16-25 of pregnancy and analyzed for steady-state SLPI mRNA levels. Endometrium situated directly beneath conceptuses (mesometrial) had greater (p < 0.05) SLPI mRNA levels than that obtained from antimesometrial and interimplantation sites and myometrium. This site-specific difference was most pronounced during late (Days 19-21) and post (Days 23-25)-implantation stages and was also observed, albeit to a lesser degree, for the mRNA encoding uteroferrin (Uf). Conditioned medium (CM; 50% v:v) from Day 21, but not Day 12, conceptuses increased (p < 0.05) SLPI mRNA levels, while neither CM affected mRNA levels for Uf and several other genes expressed in endometrial explants. One inducing factor in Day 21 CM was characterized as a low-molecular-mass (< 12 kDa), relatively heat-stable protein. Transforming growth factor (TGF alpha) increased (p < 0.05), epidermal growth factor (EGF) tended to increase (p = 0.10), and insulin-like growth factor (IGF)-I and IGF-II had no effect (p > 0.10) on, SLPI mRNA levels in Day 12 endometrial explants. Medium conditioned by the pig trophoblast cell line, Jag-1, but not by other mammalian cell lines, had SLPI inducer activity. The maternal endocrine contribution to SLPI gene expression was examined using freshly isolated and short-term-cultured Day 12 and Day 21 pregnant pig endometrium. Steady-state SLPI mRNA levels were increased (p < 0.05) in Day 12, but not Day 21, tissues upon short-term culture in serum-free medium. This increase was time dependent, was similarly demonstrated for Uf mRNA, was not observed in corresponding lung and liver, and was inhibited by inclusion of serum from pigs of diverse endocrine status. In summary, two potential modulators of endometrial SLPI gene expression were identified: 1) a conceptus-derived low-molecular-mass protein, possibly TGF alpha, that mediates in part the up-regulation of SLPI gene expression in endometrium closely associated with implantation sites, and 2) an inhibitory component(s) present in maternal serum. Results suggest opposing actions of maternal and embryonic factors at the maternal-embryo interface and highlight involvement of the periimplantation embryo in directing the spatiotemporal expression of endometrial genes implicated in its development.  相似文献   
996.
We report our experience with 2 cases in which we used the native ascending aorta and a porcine valve to reconstruct the right ventricular outflow tract in the Ross procedure. Unfortunately, in many parts of the world, the lack of homografts for reconstruction of the right ventricular outflow tract limits the use of the Ross procedure. The technique described herein can be an alternative to a cryopreserved pulmonary homograft replacement for adult patients.  相似文献   
997.
998.
Apoptosis induced by Fas (CD95) ligation is frequently lost during tumor progression; however, there is no direct evidence to support an association of Fas loss-of-function with metastatic tumor behavior. To determine whether Fas loss-of-function is critical for acquisition of the metastatic phenotype, we have compared the ability of Fas-sensitive K1735 murine melanomas to form spontaneous lung metastases in wild-type and Fas ligand-deficient mice. Fas-sensitive melanoma clones are highly tumorigenic but rarely metastatic in wild-type syngeneic mice. However, in Fas ligand-deficient mice, both the incidence and number of metastases are increased. These findings provide the first evidence that Fas-Fas ligand interactions can suppress metastasis and that tumor Fas loss-of-function may be causally linked to metastatic progression.  相似文献   
999.
Seventy-four total hip arthroplasties in sixty-six patients were performed, between 1983 and 1986, with use of a Tri-Lock femoral component inserted without cement. This tapered cobalt-chromium component has a fixed head and a circumferential proximal porous coating. Follow-up was conducted with use of a questionnaire, physical examination, and radiographic analysis. At the time of the latest follow-up, fifteen patients (eighteen hips) had died, three patients (four hips) had been lost to follow-up, and one patient (one hip) had refused to participate in the follow-up study; however, the status of fifteen hips at the time of death could be verified. Thus, clinical follow-up data were available for sixty-six of the original seventy-four hips. The average age at the time of the operation was sixty-two years (range, seventeen to eighty-four years), and the average interval between the operation and the latest follow-up evaluation was 10.0 years (range, 8.3 to 11.6 years). The Harris hip score was determined for forty-three hips (forty-one patients) in which the prosthesis was in situ at the time of the latest follow-up. The score was good for thirteen hips and excellent for twenty-eight, so the rate of clinical success was 95 per cent. Two patients had a fair result. One of them had persistent pain and the other had limited motion, but neither had radiographic evidence of loosening of the femoral or acetabular component. All forty-one patients were satisfied with the result. The probability (with standard error) of survival of the femoral component at ten years, with revision as the end point, was 0.95 +/- 0.03. The rate of revision of the femoral component because of aseptic loosening was one (2 per cent) of sixty-six. The overall rate of aseptic loosening of the femoral component in the hips that were followed radiographically was two (4 per cent) of forty-seven. Only one (2 per cent) of the forty-seven acetabular cups had evidence of aseptic loosening. There was no radiographic evidence of distal osteolysis around the prostheses that were well fixed. Proximal osteolysis was present in five (11 per cent) of forty-seven hips, but none of the lesions compromised the stability of the prosthesis or the bone and there were no associated fractures. At an average of ten years postoperatively, the Tri-Lock femoral component functioned well overall and patient satisfaction was high.  相似文献   
1000.
Induced coherent radiation (superradiance) from a subnanosecond electron bunch in a combined decelerating system has been investigated experimentally. In a first section formed by a periodically modulated waveguide, the density of the bunch is modulated and it then radiates in a second section formed by a waveguide partially filled with a dielectric. At an electron energy of 250 keV and a peak current of 800 A, millimeter radiation pulses with powers up to 2 MW and lengths up to 800 ps were obtained. Pis’ma Zh. Tekh. Fiz. 23, 14–19 (December 26, 1997)  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号