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   480841篇
  免费   4507篇
  国内免费   1029篇
电工技术   8247篇
综合类   247篇
化学工业   76052篇
金属工艺   23776篇
机械仪表   16470篇
建筑科学   10286篇
矿业工程   4766篇
能源动力   9912篇
轻工业   33564篇
水利工程   6407篇
石油天然气   16367篇
武器工业   36篇
无线电   47296篇
一般工业技术   105802篇
冶金工业   75771篇
原子能技术   15376篇
自动化技术   36002篇
  2021年   4350篇
  2019年   4146篇
  2018年   7973篇
  2017年   8146篇
  2016年   8608篇
  2015年   4933篇
  2014年   8452篇
  2013年   20137篇
  2012年   12685篇
  2011年   16325篇
  2010年   13288篇
  2009年   15020篇
  2008年   15446篇
  2007年   14997篇
  2006年   12775篇
  2005年   11625篇
  2004年   11143篇
  2003年   10712篇
  2002年   10656篇
  2001年   10388篇
  2000年   10069篇
  1999年   9582篇
  1998年   20548篇
  1997年   15683篇
  1996年   12051篇
  1995年   9432篇
  1994年   8619篇
  1993年   8666篇
  1992年   6934篇
  1991年   6990篇
  1990年   6940篇
  1989年   6816篇
  1988年   6616篇
  1987年   6021篇
  1986年   5937篇
  1985年   6637篇
  1984年   6399篇
  1983年   5980篇
  1982年   5644篇
  1981年   5807篇
  1980年   5685篇
  1979年   5798篇
  1978年   6044篇
  1977年   6490篇
  1976年   7927篇
  1975年   5458篇
  1974年   5389篇
  1973年   5481篇
  1972年   4832篇
  1971年   4447篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
This article presents the results of a pilot-study conducted on a small sample of women with breast cancer and the members of their social support system. The purpose was to determine the potential link between the mental health of the breast cancer patient and their support system. Mental health was assessed with the SCL-90-R (Derogatis, 1977), a self-report scale composed of 90 items divided into nine categories, offering three global indicators of distress: the Global Severity Index (GSI); the Positive Symptom Distress Index (PSDI), and the Positive Symptom Total (PST). The SCL-90-R was distributed to a sample of 14 subjects: seven women treated for breast cancer and seven significant others (social support). The results led to the definition of symptoms such as hostility, phobic anxiety and psychosis specific to either the woman or the support system.  相似文献   
162.
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 11, pp. 17–18, 23, November, 1993.  相似文献   
163.
SCG10 is a neuron-specific, membrane-associated protein that is highly concentrated in growth cones of developing neurons. Previous studies have suggested that it is a regulator of microtubule dynamics and that it may influence microtubule polymerization in growth cones. Here, we demonstrate that in vivo, SCG10 exists in both phosphorylated and unphosphorylated forms. By two-dimensional gel electrophoresis, two phosphoisoforms were detected in neonatal rat brain. Using in vitro phosphorylated recombinant protein, four phosphorylation sites were identified in the SCG10 sequence. Ser-50 and Ser-97 were the target sites for protein kinase A, Ser-62 and Ser-73 for mitogen-activated protein kinase and Ser-73 for cyclin-dependent kinase. We also show that overexpression of SCG10 induces a disruption of the microtubule network in COS-7 cells. By expressing different phosphorylation site mutants, we have dissected the roles of the individual phosphorylation sites in regulating its microtubule-destabilizing activity. We show that nonphosphorylatable mutants have increased activity, whereas mutants in which phosphorylation is mimicked by serine-to-aspartate substitutions have decreased activity. These data suggest that the microtubule-destabilizing activity of SCG10 is regulated by phosphorylation, and that SCG10 may link signal transduction of growth or guidance cues involving serine/threonine protein kinases to alterations of microtubule dynamics in the growth cone.  相似文献   
164.
This paper focuses on the hydrodynamics of third sound on a superfluid 3 He film. We solve the hydrodynamical equations in the limit of thick films with weak interaction with the substrate. The surface tension at the free interface is shown to have a large effect on the third sound velocity and on the attenuation for frequencies larger than 1Hz. In the case of a diffusely scattering substrate a ripplon-like dispersion relation is found for this frequency range.  相似文献   
165.
Roos  G. Hoefflinger  B. 《Electronics letters》1993,29(24):2103-2104
A process-inherent NAND2 device is presented for a three-dimensional CMOS integration with epitaxial lateral overgrowth and chemo-mechanical polishing. The required 'OR' function of the two PMOS transistors is achieved by one silicon volume, which is controlled by a back gate and a conventional front gate. Almost symmetrical characteristics are measured for the front and the back gates.<>  相似文献   
166.
167.
Data from the past few years have shown that as caffeine metabolizes solely in the liver, caffeine elimination can serve as a liver function test. We have collected data by monitoring 40 persons with liver diseases (11 chronic alcoholic hepatitis, 24 liver cirrhosis, 5 non-cirrhotic liver disease). Eight subjects served as controls. The patients with liver cirrhosis were classified according to the Child--Pugh scoring system. To determine caffeine elimination blood samples were collected before and at 3, 6, 9 and 12 hours after oral administration of 0.2 g caffeine. Fasting serum caffeine concentration and concentration 12 hours after administration, serum clearance, half life, peak concentration and volume of distribution have been compared. The respective values measured in patients with non-cirrhotic liver diseases did not differ significantly from the controls. The disappearance of caffeine was significantly decreased in cirrhotics. Our results demonstrated a good correlation between impairment of caffeine elimination and assessment of severity of liver disease by the Child--Pugh classification. Measuring serum levels in samples taken 12 hours after caffeine administration is a simple and useful method in the diagnosis of liver diseases at cirrhotic stage.  相似文献   
168.
Within the framework of the distinction between episodic and semantic memory, it has been argued that these two memory systems are organised in a hierarchical way. The hierarchical hypothesis assumes that episodic memory is a specific subsystem of semantic memory and therefore implies that episodic memory cannot exist without semantic memory. If this hypothesis is correct, it should be expected that patients with impaired semantic memory also have impaired episodic memory. In the present study, two experiments investigated the influence of semantic encoding on recognition memory performance in a population of 20 patients with Alzheimer's disease and 18 normal controls. Both experiments assessed recognition memory for semantically-related items. In Experiment 2, but not in Experiment 1, subjects were explicitly instructed to make a semantic association between the items. Alzheimer's disease patients were impaired, compared to the normal controls, on the recognition memory performance of both experiments. The ability to make a semantic association between two items was significantly and positively correlated with the subjects' performance on the recognition tasks. A further analysis showed that patients who were impaired on the semantic association task did significantly worse on the recognition task of Experiment 2 than normal controls and patients who were unimpaired on the semantic association task. These findings are discussed in the context of memory deficits in Alzheimer's disease, and are interpreted as supporting the view that episodic memory for an item is affected by the level of semantic awareness of that same item.  相似文献   
169.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
170.
The theory of interaction of charged particle beams with 2D electron gas, located in the field of the delta-like potential wallU(y) =U oδ(y) has been developed. The kinetic equation for plasmons in 2D electron gas was obtained; the conditions of arising of their instability are given and the corresponding expressions for the increment of plasmons are found.  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