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   529079篇
  免费   8248篇
  国内免费   1468篇
电工技术   9592篇
综合类   532篇
化学工业   79730篇
金属工艺   20097篇
机械仪表   15257篇
建筑科学   12922篇
矿业工程   2274篇
能源动力   14590篇
轻工业   47699篇
水利工程   5254篇
石油天然气   9351篇
武器工业   37篇
无线电   60161篇
一般工业技术   102409篇
冶金工业   104490篇
原子能技术   10574篇
自动化技术   43826篇
  2022年   3245篇
  2021年   5016篇
  2020年   3544篇
  2019年   4638篇
  2018年   7897篇
  2017年   7684篇
  2016年   8048篇
  2015年   5641篇
  2014年   9395篇
  2013年   24327篇
  2012年   14833篇
  2011年   20428篇
  2010年   15998篇
  2009年   17865篇
  2008年   18301篇
  2007年   17955篇
  2006年   15713篇
  2005年   14337篇
  2004年   13735篇
  2003年   13526篇
  2002年   12759篇
  2001年   12922篇
  2000年   11942篇
  1999年   12664篇
  1998年   32945篇
  1997年   22995篇
  1996年   17540篇
  1995年   13100篇
  1994年   11351篇
  1993年   11035篇
  1992年   7969篇
  1991年   7467篇
  1990年   7328篇
  1989年   7064篇
  1988年   6514篇
  1987年   5810篇
  1986年   5693篇
  1985年   6306篇
  1984年   5952篇
  1983年   5199篇
  1982年   4940篇
  1981年   4988篇
  1980年   4741篇
  1979年   4653篇
  1978年   4439篇
  1977年   5359篇
  1976年   7014篇
  1975年   3825篇
  1974年   3569篇
  1973年   3682篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
955.
The data of literature about the structure of cytoskeleton proteins in the normal and malignant cells are analyzed. The possibilities of using a specific polyclonal serum and a monoclonal antibody for a more precise ascertainment of the origin and diagnostic of tumours are discussed. The intermediate and active filaments may be used as a new class of histochemical markers. Laminin, the protein of basement membranes, probably, plays an important role in metastatic spreading.  相似文献   
956.
The role played by technology as a discrete independent variable in shaping the design of work is explored. The concept of coupling is developed and an empirical study of work with advanced manufacturing technology (AMT), using measurement scales derived from this concept, is outlined. Results indicate that operators of tightly coupled AMT perceive stronger supervisory influence on their working methods and show signs of lower intrinsic job satisfaction and poorer mental health than operators of more loosely coupled AMT. Implications for job redesign are discussed.  相似文献   
957.
Summary The problem of fairly densily packed particles with rate independent though otherwise arbitrary interaction is investigated in two dimensions. It is shown that slow changes in a statistically uniform medium in the pre-failure deformation state can be described by a stiffness tensor. An approximate expression for this tensor is obtained from first principles. The connection with the perfectly random heterogeneous medium is established. A simple example for round rough particles in an isotropic packing of four contacts is given.With 8 Figure  相似文献   
958.
First lactation records of 9941 Alpine, 2383 LaMancha, 11,203 Nubian, 3714 Saanen, and 4649 Toggenburg dairy goat does were obtained from the USDA to evaluate relation of registration (purebred, American, or grade) with lactation yield traits (mature equivalent milk and fat yields) and with reason for termination of lactation (normal, sold for dairy, or culled). Does were grouped by age at first kidding (11 through 16 mo or 21 through 26 mo) and by calendar year (1976 through 1978, 1979 through 1981, or 1982 through 1984). Data were analyzed within breed and year group for yield traits and within breed for reason of termination. Registration and age at first kidding accounted for little variation in mature equivalent milk and fat yields or in reason for termination.  相似文献   
959.
A new technique for exciting nonlinear waves on a charged surface of liquid hydrogen is described. Methods of optical detection of surface oscillations in experiments on capillary turbulence at frequencies of up to 10 kHz are discussed. The results of a study of capillary waves on the surface of liquid hydrogen are presented.  相似文献   
960.
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment.  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