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   362754篇
  免费   4480篇
  国内免费   1224篇
电工技术   6445篇
综合类   238篇
化学工业   56583篇
金属工艺   16962篇
机械仪表   11473篇
建筑科学   8077篇
矿业工程   2820篇
能源动力   8940篇
轻工业   27827篇
水利工程   4364篇
石油天然气   9950篇
武器工业   24篇
无线电   39218篇
一般工业技术   74279篇
冶金工业   64192篇
原子能技术   9965篇
自动化技术   27101篇
  2021年   3201篇
  2019年   3096篇
  2018年   5453篇
  2017年   5442篇
  2016年   5828篇
  2015年   3615篇
  2014年   6146篇
  2013年   15761篇
  2012年   9652篇
  2011年   12824篇
  2010年   10331篇
  2009年   11691篇
  2008年   11803篇
  2007年   11655篇
  2006年   10037篇
  2005年   9288篇
  2004年   8671篇
  2003年   8248篇
  2002年   8059篇
  2001年   8131篇
  2000年   7695篇
  1999年   7850篇
  1998年   19593篇
  1997年   13884篇
  1996年   10633篇
  1995年   8038篇
  1994年   6933篇
  1993年   7091篇
  1992年   5284篇
  1991年   5260篇
  1990年   5042篇
  1989年   5001篇
  1988年   5006篇
  1987年   4365篇
  1986年   4404篇
  1985年   4972篇
  1984年   4632篇
  1983年   4343篇
  1982年   3957篇
  1981年   3971篇
  1980年   3905篇
  1979年   3931篇
  1978年   3917篇
  1977年   4331篇
  1976年   5292篇
  1975年   3515篇
  1974年   3381篇
  1973年   3519篇
  1972年   3060篇
  1971年   2790篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
ABSTRACT: The objective of this work was to observe the microstructure of feta cheese using confocal scanning laser microscopy. Low fat cheese and cheese containing capsule-producing cultures were made. The protein network was observed using the reflectance mode of the confocal microscope. Fat was stained by Nile red dye diluted with whey. More even distribution of fat with a larger number of smaller globules was observed in cheese made with noncapsule-forming culture compared to that made with the capsule-forming culture. Nonfat cheese had compact structure when made with noncapsule-forming culture which contrasted with the open structure observed in cheese made with the capsule-forming culture  相似文献   
202.
Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus.  相似文献   
203.
Kutz  J.N. Wai  P.K.A. 《Electronics letters》1998,34(6):522-523
Based on a variational analysis, the authors demonstrate that the noise-induced Gordon-Haus timing jitter in a dispersion-managed soliton transmission system can be substantially reduced by appropriate placement of the amplifiers  相似文献   
204.
205.
206.
Although the precise pathoetiology of Beh?et's disease (BD) remains obscure, patients with BD have a high incidence of chronic infectious foci, indicating an enhanced susceptibility to chronic tonsillitis, and dental caries. Sometimes, clinical symptoms appear after treatment of these foci in BD patients. It is believed that BD might be related to an allergic reaction to a bacterial infection in view of the many clinical symptoms, especially the presence of aphthous and genital ulcerations. An attempt to obtain cutaneous responses to bacterial antigens has been carried out using various vaccines developed from bacteria isolated from the ulcerative lesions and oral cavities of BD patients. BD patients often show intense hypersensitivity to various strains of streptococci, not only by their cutaneous reactions but also by in vitro testing. In this report, we describe our previous studies on the correlation between streptococcal antigens and the pathogenesis of BD and also discuss the recent reports of other authors. The intense hypersensitivity to streptococcal antigens acquired after streptococcal infection is thought to play an important role in the appearance of symptoms in BD patients since the production of pro-inflammatory cytokines by peripheral blood mononuclear cells (PBMC) was enhanced when stimulated with streptococcal antigen in a culture system. Minocycline, an antibiotic to which certain strains of streptococci are sensitive, reduced the frequency of clinical symptoms in BD patients as well as the production of pro-inflammatory cytokines by BD-PBMC stimulated with streptococcal antigen.  相似文献   
207.
208.
Pigmented vulvar lesions were observed in a child during a sexual abuse evaluation. Gross examination of the lesions appeared most consistent with bowenoid papulosis; however, biopsy confirmed the lesions to be pigmented apocrine hamartomas. To our knowledge, these rare and benign tumors have never been described as pigmented, but should be added to the differential diagnosis of pigmented vulvar lesions.  相似文献   
209.
Estramustine is an estradiol-based agent that has been shown to accumulate in human glioma cells, resulting in a concentration-dependent alteration in cell size and shape within minutes and an inhibition of proliferation over 3 to 6 days. We evaluated human glioblastoma cultures with [3H]thymidine incorporation assays to determine estramustine's early effects on deoxyribonucleic acid synthesis in these tumors. Because estramustine shares a common structural motif with other antimicrotubule drugs, we synthesized four A-ring conjugates of estrone that contained a carbamate moiety but lacked nitrogen mustard. These analogs were examined by [3H]thymidine incorporation and compared with vinblastine. Greater than 70% inhibition of [3H]thymidine incorporation occurred within 1 hour of treatment with estramustine at 10(-5) mol/L, which increased to 80% inhibition at 4 hours. Ethyl carbamate JE208 was nearly as effective as estramustine in inhibiting deoxyribonucleic acid synthesis, and both were more effective than vinblastine. The inhibitory effects of estramustine and estrone analogs were reversible; vinblastine was not reversible. Although estramustine and JE208 induced similar antiproliferative and morphological changes in glioblastoma cells that persisted for at least 4 days, there was a modest recovery of morphology and thymidine incorporation with JE208 after prolonged treatment. The common findings with estramustine and JE208 suggest that these agents may have a similar mechanism of action and form the basis for the investigation of new agents that may rapidly and reversibly inhibit glioblastoma.  相似文献   
210.
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