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   104182篇
  免费   6217篇
  国内免费   933篇
电工技术   1878篇
技术理论   1篇
综合类   1426篇
化学工业   20560篇
金属工艺   2808篇
机械仪表   2835篇
建筑科学   4278篇
矿业工程   728篇
能源动力   2813篇
轻工业   13507篇
水利工程   1055篇
石油天然气   1689篇
武器工业   125篇
无线电   6886篇
一般工业技术   16316篇
冶金工业   19601篇
原子能技术   752篇
自动化技术   14074篇
  2024年   160篇
  2023年   990篇
  2022年   1580篇
  2021年   2975篇
  2020年   2139篇
  2019年   2222篇
  2018年   3354篇
  2017年   3456篇
  2016年   3556篇
  2015年   3022篇
  2014年   3990篇
  2013年   6968篇
  2012年   6018篇
  2011年   6328篇
  2010年   5015篇
  2009年   4847篇
  2008年   4753篇
  2007年   4263篇
  2006年   3693篇
  2005年   3184篇
  2004年   2686篇
  2003年   2414篇
  2002年   2269篇
  2001年   1583篇
  2000年   1582篇
  1999年   1816篇
  1998年   6248篇
  1997年   4124篇
  1996年   2850篇
  1995年   1780篇
  1994年   1472篇
  1993年   1434篇
  1992年   627篇
  1991年   591篇
  1990年   485篇
  1989年   482篇
  1988年   469篇
  1987年   393篇
  1986年   375篇
  1985年   406篇
  1984年   348篇
  1983年   257篇
  1982年   332篇
  1981年   343篇
  1980年   319篇
  1979年   228篇
  1978年   210篇
  1977年   512篇
  1976年   1063篇
  1973年   159篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation.  相似文献   
52.
Costunolide (CE) and dehydrocostuslactone (DE) are derived from many species of medicinal plants, such as Saussurea lappa Decne and Laurus nobilis L. They have been reported for their wide spectrum of biological effects, including anti-inflammatory, anticancer, antiviral, antimicrobial, antifungal, antioxidant, antidiabetic, antiulcer, and anthelmintic activities. In recent years, they have caused extensive interest in researchers due to their potential anti-cancer activities for various types of cancer, and their anti-cancer mechanisms, including causing cell cycle arrest, inducing apoptosis and differentiation, promoting the aggregation of microtubule protein, inhibiting the activity of telomerase, inhibiting metastasis and invasion, reversing multidrug resistance, restraining angiogenesis has been studied. This review will summarize anti-cancer activities and associated molecular mechanisms of these two compounds for the purpose of promoting their research and application.  相似文献   
53.
54.
Combined photochemical arylation, “nuisance effect” (SNAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with SNAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.  相似文献   
55.
56.
This study deals with the formulation of natural drugs into hydrogels. For the first time, compounds from the sage essential oil were formulated into chitosan hydrogels. A sample preparation procedure for hydrophobic volatile analytes present in a hydrophilic water matrix along with an analytical method based on the gas chromatography coupled with the mass spectrometry (GC-MS) was developed and applied for the evaluation of the identity and quantity of essential oil components in the hydrogels and saline samples. The experimental results revealed that the chitosan hydrogels are suitable for the formulation of sage essential oil. The monoterpene release can be effectively controlled by both chitosan and caffeine concentration in the hydrogels. Permeation experiment, based on a hydrogel with the optimized composition [3.5% (w/w) sage essential oil, 2.0% (w/w) caffeine, 2.5% (w/w) chitosan and 0.1% (w/w) Tween-80] in donor compartment, saline solution in acceptor compartment, and semi-permeable cellophane membrane, demonstrated the useful permeation selectivity. Here, (according to lipophilicity) an enhanced permeation of the bicyclic monoterpenes with antiflogistic and antiseptic properties (eucalyptol, camphor and borneol) and, at the same time, suppressed permeation of toxic thujone (not exceeding its permitted applicable concentration) was observed. These properties highlight the pharmaceutical importance of the developed chitosan hydrogel formulating sage essential oil in the dermal applications.  相似文献   
57.
58.
59.
60.
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