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   1453篇
  免费   5篇
  国内免费   1篇
电工技术   3篇
化学工业   52篇
金属工艺   13篇
机械仪表   4篇
建筑科学   18篇
矿业工程   1篇
能源动力   2篇
轻工业   57篇
水利工程   6篇
石油天然气   4篇
无线电   43篇
一般工业技术   67篇
冶金工业   1110篇
原子能技术   1篇
自动化技术   78篇
  2022年   3篇
  2021年   4篇
  2020年   5篇
  2019年   3篇
  2018年   7篇
  2017年   3篇
  2016年   4篇
  2013年   19篇
  2012年   8篇
  2011年   14篇
  2010年   6篇
  2009年   7篇
  2008年   16篇
  2007年   12篇
  2006年   16篇
  2005年   12篇
  2004年   11篇
  2003年   23篇
  2002年   15篇
  2001年   12篇
  2000年   19篇
  1999年   39篇
  1998年   320篇
  1997年   208篇
  1996年   131篇
  1995年   66篇
  1994年   71篇
  1993年   80篇
  1992年   17篇
  1991年   13篇
  1990年   11篇
  1989年   13篇
  1988年   17篇
  1987年   11篇
  1986年   16篇
  1985年   19篇
  1984年   5篇
  1983年   9篇
  1982年   10篇
  1981年   9篇
  1980年   22篇
  1978年   9篇
  1977年   34篇
  1976年   77篇
  1974年   4篇
  1972年   3篇
  1971年   3篇
  1968年   4篇
  1965年   2篇
  1955年   2篇
排序方式: 共有1459条查询结果,搜索用时 0 毫秒
11.
1. Occupational health nurses need a general knowledge of psychiatric medications to work effectively with clients and their off site health providers. 2. Acquiring an understanding of the major classes of medications--anti-psychotic, anti-anxiety, anti-depressant, and antimanic--is important. 3. It is helpful to understand under what conditions and with which conditions psychotropic medications are helpful.  相似文献   
12.
13.
A method for simultaneously engineering multiple properties of a protein, based on the observed additivity of effects of individual mutations, is presented. We show that, for the gene V protein of bacteriophage f1, effects of double mutations on both protein stability and DNA binding affinity are approximately equal to the sums of the effects of the constituent single mutations. This additivity of effects implies that it is possible to deliberately construct mutant proteins optimized for multiple properties by combination of appropriate single mutations chosen from a characterized library.  相似文献   
14.
Reviews the book, Child sexual abuse: Critical perspectives on prevention, intervention, and treatment edited by Christopher R. Bagley and Ray J. Thomlison (1991). This book is a compilation of a series of literature reviews originally commissioned by Health and Welfare Canada in 1987 and completed in 1988. The individual papers included in this edited version represent a cross section of Canadian academicians, clinicians, and case workers who are integrally involved in the policies and practices regarding child sexual abuse in Canada. The work provides a comprehensive perspective on prevention at the primary, secondary, and tertiary levels. The list of authors is impressive in terms of their expertise and experience. At a time when numerous books on child sexual abuse are appearing on the market, it is nice to see a book that has some unusual aspects. Aside from its distinctly Canadian perspective, the book addresses several important, yet frequently ignored, topics. The book provides an up-to-date review of several core issues: conceptualization of the problem, prevention strategies, impact of sexual abuse, investigative interviewing, treatment outcome studies, and treatment issues for child molesters. The more unique topics include a review of the strategies used to evaluate prevention programs, prevalence rates among a number of special populations, the role of medical practitioners in preventing and intervening in child sexual abuse, and sexual abuse and exploitation among disabled individuals. Overall, I can recommend this book for clinicians and researchers in Canada and elsewhere who are interested in child sexual abuse. This compilation of literature reviews highlights the leading role that Canadian social service agencies have taken in developing programs for sexually abused children and their families. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
15.
Anecdotal reports suggest cattle with fescue toxicosis may not respond to vaccination and thus, experience increased incidence of Bovine Respiratory Disease Complex (BRDC) when shipped to feedlots. Fescue toxicosis causes hypoprolactemia in cattle. Hypoprolactemia decreases humoral immune responses in mice. Therefore, a study was conducted to compare the magnitude of primary and secondary humoral immune responses against specific antigens in cattle grazing endophyte-infected or endophyte-free fescue. Angus steers were blocked by weight and allocated into four groups. Two groups grazed endophyte-infected (EI) fescue and the other two groups grazed endophyte-free (EF) fescue. All steers were injected IM on d 0 and 21 with lysozyme without adjuvant and concanavalin. A (Con A) with sheep red blood cells (SRBC) in incomplete adjuvant of Freund. Steers were bled on days 0, 21 and 35 post-vaccination. Average daily gains (ADG), alkaline phosphatase (ALP) activity, cholesterol concentrations, rectal temperatures, and serum prolactin concentrations were measured to confirm fescue toxicosis in steers grazing EI fescue. Antibodies to Con A and SRBC were determined by ELISA and hemagglutination assay, respectively. The ADG were decreased for the EI group during the first month. Rectal temperature were elevated and serum prolactin concentrations were decreased in the EI group. Cholesterol and ALP concentrations also were decreased in the EI group. Primary and secondary immune responses against Con A tended to be increased and were increased against SRBC in the EI group. Antibodies against lysozyme were not induced in either group. In conclusion, cattle grazing EI fescue mounted similar humoral immune responses to vaccination, despite hypoprolactemia, as cattle grazing EF fescue. Increases in bovine respiratory disease in cattle maintained on EI fescue probably is not associated with lack of humoral immune response to vaccination protocols as a result of fescue toxicosis.  相似文献   
16.
A 73-year-old male was admitted to our hospital because of detection of Shigella flexneri 2a from his stool. Antimicrobial treatment with levofloxacin (LVFX) was started, but could not eliminate the organism in the stool. In the examination of drug susceptibility, this strain was highly resistant to all new quinolones. The minimal inhibitory concentration of norfloxacin, ofloxacin and ciprofloxacin to this strain was 12.5 micrograms/ml, 6.25 micrograms/ml and 6.25 micrograms/ml, respectively. The dual mutations were detected in the codon 83 and 87 of the gyrA gene by sequencing the quinolone-resistance determining region (QRDR). There was, however, no significant difference between the intracellular uptake of ciprofloxacin in this strain and in the ciprofloxacin-sensitive strain. The amount of ciprofloxacin in this strain unchanged when carbonyl cyanide m-chlorophenyl hydrazone (CCCP) was added. These results suggest that the advanced resistance in Shigella flexneri against new quinolones could be acquired by only this dual mutations without the change of the active efflux mechanism.  相似文献   
17.
Recent research on annotation interfaces provides provocative evidence that anchored, annotation-based discussion environments may lead to better conversations about a text. However, annotation interfaces raise complicated tradeoffs regarding screen real estate and positioning. It is argued that solving this screen real estate problem requires limiting the number of annotations displayed to users. In order to understand which annotations have the most learning value for students, this paper presents two complementary studies examining the effects of annotations on students performing a reading-to-write task. The first study used think-aloud protocols and a within-subjects methodology, finding that annotations appeared to provoke students to reflect more critically upon the primary text. This effect was particularly strong when students encountered pairs of annotations presenting different viewpoints on the same section of text. Student interviews suggested that annotations were most helpful when they caused the reader to consider and weigh conflicting viewpoints. The second study used a between-subjects methodology and a more naturalistic task to provide complementary evidence that annotations encourage more reflective responses to a text. This study found that students who received annotated materials both perceived themselves and were perceived by instructors as less reliant on unreflective summary strategies than students who received the same content but in a different format. These findings indicate that the learning value of an annotation lies in its ability to provoke students to consider and weigh new perspectives on the primary text. When selected effectively, annotations provide a critical scaffolding that can support students’ critical thinking and argumentation activities. Collaborative digital libraries and applications for the Web 2.0 should be designed with this learning framework in mind.  相似文献   
18.
19.
OBJECTIVE: The initially well-fixed implants of total hip replacement (THR) are in the long-term subject to aseptic loosening. Many cytokines can contribute to osteolysis due to osteoclast recruitment and/or activation. However, in this respect tumor necrosis factor-alpha (TNF-alpha) plays a pivotal role, because it upregulates interleukin-1 and 6 and granulocyte-macrophage colony stimulating factor. The aim of this study was to assess the eventual presence, cellular localization and extent of expression of TNF-alpha in the synovial-like membrane at the implant or at the cement to bone interface compared to control synovial membrane. METHODS: Twenty samples from the synovial-like membrane of the periprosthetic tissues were compared to control samples. TNF-alpha containing cells were visualized using an avidin-biotin-peroxidase complex (ABC) method and analyzed by light microscopy, double labelling and image analysis. RESULTS: TNF-alpha was found in the periprosthetic tissues in fibroblasts and vascular endothelial cells, but mainly in the macrophages was it found to coincide with areas containing implant-derived debris. TNF-alpha containing cells were more numerous in the synovial-like membrane in the interface tissue from the proximal stem area (2816 +/- 318 cells) than in the control synovial membrane (565 +/- 93 cells, p < 0.01). Interestingly, similarly high TNF-alpha expression (3452 +/- 582 cells) was also seen in the synovial-like membrane of the pseudocapsule. CONCLUSION: These findings suggest that the foreign body-type host reaction caused by THR is characterized by the high expression of TNF-alpha. Because such expression occurred in the interface tissue between the implant and surrounding bone, TNF-alpha, due to its pivotal direct and indirect role in the activation and recruitment of osteoclasts, may contribute to periprosthetic osteolysis and to the loosening of THR.  相似文献   
20.
In order to test the hypothesis that binding sites of cholera toxin for its receptor, the monosialoganglioside GM1, are shared between adjacent beta-polypeptide chains, two inactive chemical derivatives of the B subunit of cholera toxin (CTB) were prepared and were subsequently used for the construction of hybrid CTB pentamers. One inactive derivative consisted of CTB specifically modified in the single essential Trp-88 residue of each beta-chain. This residue was modified by formylation, a treatment preserving the structural integrity of CTB. The other inactive derivative consisted of CTB specifically succinylated in three amino groups located in or near the receptor binding site. Using [1,4-14C]succinic anhydride for the site-specific succinylation and analysis of radiolabeled tryptic fragments of S-carboxymethylated [14C]sssCTB revealed that the amino groups specifically modified were the alpha-amino group of Thr-1 and the epsilon-amino groups of respectively Lys-34 and Lys-91. Upon submitting equal amounts of formylated CTB and site-specific succinylated CTB to a denaturation-renaturation cycle, hybrid pentamers were formed which in contrast to the parental compounds were able to bind GM1. The affinity of hybrid CTB for GM1, as estimated by a competitive solid-phase radiobinding assay was unexpectedly high and only 2.5-fold lower than that of its native counterpart. The number of active binding sites on hybrid CTB was determined from: (i) titration with the oligosaccharide moiety of GM1 (oligo-GM1) and monitoring the reversal of the Trp fluorescence quenching by iodide ions and (ii) rapid gel filtration over a superdex HR column of a mixture of hybrid CTB and an excess of 3H-labeled oligo-GM1. The data are in agreement with the formation of one active binding per four reconstituted binding sites in hybrid CTB, which is consistent with a random association of CTB monomers during the denaturation-renaturation cycle.  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