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   151703篇
  免费   2045篇
  国内免费   655篇
电工技术   3115篇
综合类   187篇
化学工业   24072篇
金属工艺   5781篇
机械仪表   4942篇
建筑科学   4418篇
矿业工程   377篇
能源动力   3927篇
轻工业   17306篇
水利工程   1140篇
石油天然气   618篇
武器工业   5篇
无线电   20493篇
一般工业技术   28845篇
冶金工业   23754篇
原子能技术   2341篇
自动化技术   13082篇
  2019年   834篇
  2018年   1082篇
  2017年   1131篇
  2016年   1268篇
  2015年   1063篇
  2014年   1796篇
  2013年   6575篇
  2012年   3192篇
  2011年   4608篇
  2010年   3594篇
  2009年   4151篇
  2008年   4647篇
  2007年   4913篇
  2006年   4350篇
  2005年   4108篇
  2004年   4002篇
  2003年   3899篇
  2002年   3928篇
  2001年   3980篇
  2000年   3742篇
  1999年   3691篇
  1998年   6632篇
  1997年   5227篇
  1996年   4460篇
  1995年   3709篇
  1994年   3358篇
  1993年   3184篇
  1992年   2783篇
  1991年   2690篇
  1990年   2628篇
  1989年   2614篇
  1988年   2459篇
  1987年   2166篇
  1986年   2115篇
  1985年   2556篇
  1984年   2316篇
  1983年   2195篇
  1982年   2068篇
  1981年   1991篇
  1980年   1860篇
  1979年   1874篇
  1978年   1770篇
  1977年   2085篇
  1976年   2562篇
  1975年   1583篇
  1974年   1430篇
  1973年   1453篇
  1972年   1196篇
  1971年   1115篇
  1970年   948篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
851.
852.
加脂是软革制造过程中最重要的工序。本文建立了一个加脂过程和加脂机理的模型。在该模型中,传统的完全依赖PH值的观察被扩展,结合了加脂剂与浴液间的相互作用的性能和传送提供润滑作用的中性油组分的乳化剂的作用,并扩展了乳化剂的角色。以这种方式引入的化学柔软作用对革的强度有积极的效果,而相比效应力柔软作用会降低革的强度。  相似文献   
853.
As part of an international study initiated by the World Health Organization (WHO) about psychological disorders in primary health care, patients in the Federal Republic of Germany were compared with patients in other European centres. Patients from Germany do not differ from other European patients in respect to sociodemographic variables or psychiatric disorders. The most frequent CIDI-based diagnoses recorded in patients attending general practices are current depressive episodes (8.6%), generalized anxiety disorders (8.5%), neurasthenia (7.5%), and alcohol dependence (6.3%). In 20.9% of the patients at least one psychiatric diagnosis based on ICD-10 was recorded. In Germany significantly lower global ratings of health status are given than in other European centres although there is no difference in diagnostic prevalence rates. The recognition rate, i.e. the agreement between the CIDI-based ICD-10 diagnoses and the recognition as a case by the physician, is 56.2%-60.2%. On the other hand, the CIDI detects 90% of the patients described as psychologically ill by the physicians if subthreshold cases are also counted, or 46.4% if only defined diagnoses are taken into account. There is a significant correlation between severity of the psychiatric disorder and disability in social functioning. In Mainz and in the other European countries the disability rate of patients with a well-defined disorder is between 67.0% and 72.7%, whereas in Berlin this relation is not as clear, because especially in East Berlin there is a higher rate of unemployment in view of the political situation. Drug treatment is prescribed for 16.1% of the patients in primary care for psychiatric disorders. Half the patients recognized by physicians as cases receive medication. In the rest of Europe patients receive significantly more tranquillizers than in Germany, where the use of herbal drugs is more wide spread.  相似文献   
854.
Heterotrimeric GTP-binding proteins (G-proteins) have been shown to play an important role in cellular signalling. However, G-protein involvement in the intracellular spreading of bacterial pathogens is still poorly understood. In this study, antibodies, that recognize G-protein alpha-subunits (anti-G alpha), were used to investigate the localization of G-proteins in the macrophage-like cell line P388D1 and E. coli, also in their L-forms, during phagocytosis. In E. coli, anti-G alpha-binding sites were detected preferably in the cell wall and septa of the whole bacterial forms as well as in the cytoplasm of L-forms. Western blotting of bacterial lysates demonstrated protein bands with positive immunoreaction to antibodies against Gs alpha, Gi alpha, and Gcommon alpha with a higher affinity to the antibody against Gs alpha. Immunoreaction with the anti-Gs alpha-antibody was markedly higher in pathogenic strains of E. coli. Because of the conserved structure in all GTP-binding proteins which seem to derive from a single primordial protein involved in signal transduction mechanisms, it is reasonable to assume that some anti-Ga-positive proteins in E. coli might be related to G-proteins of higher organisms. A putative candidate for bacterial G-proteins seems to be a 36 kDa protein. Enhancement in G-protein immunostaining in the cytoplasm of macrophages around the internalized bacteria testifies to the involvement of G-proteins in mediation of endocytosis responses of phagocytes.  相似文献   
855.
Timed Petri nets can be used to model and analyse scheduling problems. To support the modelling of scheduling problems, we provide a method to map tasks, resources and constraints onto a timed Petri net. By mapping scheduling problems onto Petri nets, we are able to use standard Petri net theory. In this paper we will show that we can use Petri net based tools and techniques to find conflicting and redundant precedences, upper- and lower-bounds for the makespan, etc. This is illustrated by a Petri net based analysis of the notorious 10×10 problem due to Fisher & Thompson (1963)  相似文献   
856.
The bone response to different calcium phosphate (Ca-P) coated implants was evaluated in a goat animal model. Two types of plasma spray coatings were applied to a commercially pure titanium (cpTi) tapered, conical screw-design implant (BioComp®); hydroxyapatite (HA-PS) and a dual coating, consisting of FA and HA (FA/HA-PS). In addition an amorphous RF magnetron sputter coating (Ca-P-a) and uncoated implants were investigated. Forty-eight implants were inserted in the maxilla of 12 adult female goats. After implantation periods of 3 and 6 months, the bone implant interface was evaluated histologically and histomorphometrically. After both implantation periods all plasma spray coated implants were maintained. On the other hand three Ca-P-a and two cpTi implants were lost. Histological examination revealed a better bone response to both plasma spray coated implants. Histomorphometrical evaluation confirmed this finding. At 3 and 6 months significantly higher percentages of bone contact (p<0.001, ANOVA) were measured for both plasma spray coated implants than for the cpTi and Ca-P-a implants, while no significant difference (p<0.05) existed between both implantation periods. Degradation of both plasma spray coatings was observed. Supported by the results, it is concluded that, although Ca-P coatings can improve the performance of dental implants, the presence of a Ca-P coating is not the only important factor for bone healing around implants placed in low density trabecular bone.  相似文献   
857.
Spherical dosage forms have been reported to be an efficient and effective method for delivering drugs into the body and controlling their dissolution rate. Substantial work has been conducted in these laboratories illustrating the advantages of microcrystalline cellulose-based spheres for these purposes. Through various methodologies, but most routinely the extrusion and marumerization technique, it has been determined by Funck, et al. that not more than 50% drug can be incorporated into a sphere formulation without the addition of other binders.

Because of the nature of the extrusion and marumerization manufacturing process, the type of drug being processed and the resultant particle size requirements of the spheres, the percent of spheres falling outside the desired particle size can range from between 3% and 20%. For this reason and the possibility of operator errors, our objective was to determine the parameters which needed monitoring when reprocessing was necessary.  相似文献   
858.
Software quality assurance (SQA) audits are becoming a standard practice in corporations seeking to enter contractual relations with other organizations, or just evaluating their own state of readiness. This paper describes one approach to conducting SQA audits. Excerpts from reports of actual audits conducted on several organizations engaged in software development are used to show how an audit is conducted and what can be achieved through the auditing process. The paper is not meant to be a definitive answer or guide to doing SQA audits. Rather, it serves as an annotated case study of how SQA audits can be conducted with an emphasis on data gathering and reporting.Dr Paul W. Oman is an associate professor of computer science at the University of Idaho, and an independent software consultant who specializes in software analysis. He is the director of the Software Engineering Test Lab within the UI College of Engineering, where he conducts research in software development methods, CASE tools, and software maintainability issues. Oman has published over 50 articles and reports on software tools, software development, and computer science education. He has a PhD in computer science and is a member of the IEEE, IEEE Computer Society, and ACM.  相似文献   
859.
Insulin solution (25 U/ml/kg, pH 8.0) was administered with 50 mM of various C8-Cl8 fatty acid and derivative absorption enhancers to the duodenum, colon and rectum of fasted normal rats under sodium pentobarbital anesthesia. Solutions were administered directly into ligated or sealed intestinal segments. Blood was sampled periodically from the jugular vein and blood glucose levels determined. The maximum decrease in blood glucose level and area under the depression curve were used to estimate bioavailability. Enhancing effects rectally were further investigated in streptozotocin-induced diabetic rats in both the fasted and non-fasted states. Blood glucose levels and serum insulin concentrations were determined.  相似文献   
860.
Developments are reported in both numerical and experimental capabilities for characterizing the debris spray produced in penetration events. We have performed a series of high-velocity experiments specifically designed to examine the fragmentation of the projectile during impact. High-strength, well-characterized steel spheres (6.35 mm diameter) were launched with a two-stage light-gas gun to velocities in the range of 3 to 5 km/s. Normal impact with PMMA plates, thicknesses of 0.6 to 11 mm, applied impulsive loads of various amplitudes and durations to the steel sphere. The extent of fragmentation, loss in momentum, and divergence of the debris are shown to correspond to the impact conditions. Multiple flash radiography was used to monitor material motion and fragmentation of the steel sphere during the impact event. Dynamic fragmentation theories, based on energy-balance principles, were used to evaluate local material deformation and fracture state information from CTH, a three-dimensional Eulerian solid dynamics shock wave propagation code. The local fragment characterization of the material defines a weighted fragment size distribution, and the sum of these distributions provides a composite particle size distribution for the steel sphere. The calculated axial and radial velocity changes agree well with experimental data, and the calculated fragment sizes for a specific experiment are in qualitative agreement with the radiographic data.  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