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   43899篇
  免费   958篇
  国内免费   186篇
电工技术   550篇
综合类   632篇
化学工业   4955篇
金属工艺   613篇
机械仪表   898篇
建筑科学   845篇
矿业工程   392篇
能源动力   457篇
轻工业   2107篇
水利工程   619篇
石油天然气   61篇
武器工业   4篇
无线电   1952篇
一般工业技术   3541篇
冶金工业   21504篇
原子能技术   198篇
自动化技术   5715篇
  2024年   60篇
  2023年   208篇
  2022年   152篇
  2021年   159篇
  2019年   79篇
  2018年   513篇
  2017年   725篇
  2016年   1093篇
  2015年   810篇
  2014年   465篇
  2013年   493篇
  2012年   2194篇
  2011年   2478篇
  2010年   716篇
  2009年   799篇
  2008年   635篇
  2007年   652篇
  2006年   580篇
  2005年   3361篇
  2004年   2569篇
  2003年   2058篇
  2002年   864篇
  2001年   745篇
  2000年   286篇
  1999年   630篇
  1998年   6171篇
  1997年   3824篇
  1996年   2520篇
  1995年   1458篇
  1994年   1078篇
  1993年   1115篇
  1992年   256篇
  1991年   313篇
  1990年   315篇
  1989年   294篇
  1988年   301篇
  1987年   234篇
  1986年   212篇
  1985年   176篇
  1984年   83篇
  1983年   89篇
  1982年   139篇
  1981年   187篇
  1980年   204篇
  1979年   66篇
  1978年   102篇
  1977年   614篇
  1976年   1330篇
  1975年   104篇
  1971年   53篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
301.
The sympatholytic antihypertensive agent moxonidine, a centrally acting selective I1-imidazoline receptor modulator (putative agonist), may be beneficial in hypertensive patients with insulin resistance. In the present study, the effects of chronic in vivo moxonidine treatment of obese Zucker rats--a model of severe glucose intolerance, hyperinsulinemia and insulin resistance, and dyslipidemia--on whole-body glucose tolerance, plasma lipids, and insulin-stimulated skeletal muscle glucose transport activity (2-deoxyglucose uptake) were investigated. Moxonidine was administered by gavage for 21 consecutive days at 2, 6, or 10 mg/kg body weight. Body weights in control and moxonidine-treated groups were matched, except at the highest dose, at which final body weight was 17% lower in the moxonidine-treated animals compared with controls. The moxonidine-treated (6 and 10 mg/kg) obese animals had significantly lower fasting plasma levels of insulin (17% and 19%, respectively) and free fatty acids (36% and 28%, respectively), whereas plasma glucose was not altered. During an oral glucose tolerance test, the glucose response (area under the curve) was 47% and 67% lower, respectively, in the two highest moxonidine-treated obese groups. Moreover, glucose transport activity in the isolated epitrochlearis muscle stimulated by a maximally effective insulin dose (13.3 nmol/L) was 39% and 70% greater in the 6 and 10 mg/kg moxonidine-treated groups, respectively (P<.05 for all effects). No significant alterations in muscle glucose transport were elicited by 2 mg/kg moxonidine. These findings indicate that in the severely insulin-resistant and dyslipidemic obese Zucker rat, chronic in vivo treatment with moxonidine can significantly improve, in a dose-dependent manner, whole-body glucose tolerance, possibly as a result of enhanced insulin-stimulated skeletal muscle glucose transport activity and reduced circulating free fatty acids.  相似文献   
302.
Fibroblast growth factors are important heparin binding, mitogenic proteins. The binding site in heparin and heparan sulfate for fibroblast growth factor-2 (basic fibroblast growth factor) has been described as rich in glucosamine-2-sulfate 1-->4 linked to iduronic acid-2-sulfate. The glucosamine residue in the heparin binding site is also 6-sulfated. A new glycosaminoglycan, acharan sulfate, has been chemically modified to prepare a polysaccharide, N-sulfoacharan sulfate, consisting of glucosamine-2-sulfate 1-->4 linked to iduronic acid-2-sulfate. Acharan sulfate binds very weakly to fibroblast growth factor-2 while N-sulfoacharan sulfate binds with nearly the same affinity as heparin. Mitogenicity studies were performed using heparan sulfate-free cells stably transfected with fibroblast growth factor receptor-1. Acharan sulfate inhibits heparin's enhancement of fibroblast growth factor-2 mitogenic activity, without affecting cell viability, while N-sulfoacharan sulfate shows heparin-like activity but at a greatly reduced level. These results suggest additional mechanisms not requiring high affinity glycosaminoglycan binding to fibroblast growth factor-2 may be important in its mitogenic activity.  相似文献   
303.
Samples of peripheral blood from 76 different donors were detected for the presence of human cytomegalovirus (HCMV) DNA by polymerase chain reaction (PCR). The results showed that HCMVs were present in 39 out of 76 blood donors which reached an infection positive rate of 51.3%. In addition, the sensitivity and specificity on PCR were tested, it also indicated that the sensitivity can reach the level of 5fg.microliter-1. The method is simple, rapid, highly sensitive and specificity. It can be considered as a diagnostic measure in clinical detection of HCMV.  相似文献   
304.
305.
First, annual cost of electronic filing of medical images were calculated and compared with that of film storage in two hospitals under different conditions. Storage of medical images using a pixel size of 100 microns x 100 microns and 2-byte depth on the 130 mm, 650 MB magneto-optical disks costs with four times as much as the cost for film storage. However, 175 microns x 175 microns 12 bits combined with implementation of lossless compression would reduce the cost to a level equal to that for films storage. Doubled or tripled densities of MOD will improve the cost ever further. Second, the effectiveness of Hospital Information System/Radiological Information System (HIS/RIS) was evaluated. Examination time, film delivery time and the total turn-around time was markedly shortened by more than 23 hours on average. Our measurement method employing IC cards in pre-post HIS/RIS/PACS procedures is generally applicable to other hospitals. Third, to determine the optimal method of maximizing the efficacy of diagnostic imaging, 260 questionnaires were sent to the staff of 13 university hospitals. Every situation was described by both a radiologist and the physician who ordered the examination and received the reports and images. The level of technical efficacy and diagnostic accuracy of radiology strongly influenced the diagnostic thought processes of the physician.  相似文献   
306.
If the previous restorative therapy or dental caries has resulted in substantial loss of tooth structure, the abutment teeth for fixed prosthodontic restorations require a core reconstruction or a post and core. Small dentin defects can be restored with bonded cores; more extensive dentin defects that are often accompanied by previous endodontic treatment generally require additional support for the core material. A direct procedure with a bonded post is a viable treatment method. The decision to use either light-conducting all-ceramic zirconium or titanium as a post material depends on the aesthetic requirements present. The indications for a cast post and core as an indirect procedure for prosthodontic reconstructions appear to be decreasing. The learning objective of this article is to review the past and current post and core materials and techniques. Indications for core reconstruction with vital teeth and posts and cores for pulpless teeth are discussed.  相似文献   
307.
The electrochemical behaviour of Cu-xZn alloys, as well as their constituent metals, in a borate buffer containing chloride ions in the molar range from 0.01 to 1 M are studied. Characteristics of these materials under anodic polarization are compared and the composition and morphology of the corrosion products formed in the course of polarization experiment are analysed by SEM and EDS. X-ray photoelectron spectroscopy and electrochemical impedance measurements are used for characterization of the surface layers formed on Cu, Zn and Cu-40Zn alloy during 2-h immersion at Eoc in a borate buffer containing two different concentrations of chloride ions. New aspects of the behaviour of brass under Eoc condition are revealed. The improved corrosion resistance of brass in chloride media, if compared to zinc metal, is attributed to a Cu-rich layer formed by the selective dissolution of zinc. Based on the results, a structural model describing the improved corrosion resistance of Cu-40Zn alloy with respect to Zn metal is proposed.  相似文献   
308.
Sulfoaluminate-belite (SAB) cements are an attractive class of low-energy cements from the viewpoint of saving energy and releasing less CO2 into the atmosphere during their production. Their hydraulic activity, however, does not match that of the ordinary Portland cement (PC) and needs improvement before they can be used on their own. However, SAB cements when blended with PC have the potential to be used effectively in traditional applications as shown by this study. Mortars made with blends of SAB cements and PC, and a cement-to-sand ratio of 1:3 by weight and a water-to-cement ratio of 0.5, indicate a superior protection against corrosion of steel to those made with blends of PC and blast-furnace slag (BFSPC). The prepared mortars were stored at 20 °C for 90 days under either a 60% relative humidity (RH)-dry air, or 100% RH-wet air conditions. With further improvement in the SAB cement quality through better understanding of their characteristics, a genuine competition between SAB/PC and BFSPC can be expected in practice.  相似文献   
309.
A new definition of the testability transfer factor for circuit components that provides better sensitivity with respect to parametric deviations is presented. New equations for the testability measures in a mixed-signal core are given. Testability analysis is used for test-pattern generation and for consideration of inserting wrapper cells. The simulation results show the effectiveness of the approach.  相似文献   
310.
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