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   1320篇
  免费   4篇
  国内免费   1篇
化学工业   33篇
机械仪表   2篇
建筑科学   2篇
能源动力   1篇
轻工业   18篇
石油天然气   1篇
无线电   12篇
一般工业技术   94篇
冶金工业   1153篇
原子能技术   3篇
自动化技术   6篇
  2022年   1篇
  2020年   2篇
  2019年   2篇
  2018年   2篇
  2017年   4篇
  2016年   1篇
  2014年   1篇
  2013年   16篇
  2012年   4篇
  2011年   25篇
  2010年   7篇
  2009年   10篇
  2008年   5篇
  2007年   9篇
  2006年   11篇
  2005年   9篇
  2004年   3篇
  2003年   7篇
  2002年   4篇
  2001年   4篇
  2000年   6篇
  1999年   39篇
  1998年   380篇
  1997年   206篇
  1996年   132篇
  1995年   82篇
  1994年   59篇
  1993年   76篇
  1992年   22篇
  1991年   24篇
  1990年   11篇
  1989年   19篇
  1988年   6篇
  1987年   22篇
  1986年   11篇
  1985年   8篇
  1983年   4篇
  1982年   3篇
  1981年   9篇
  1980年   3篇
  1979年   3篇
  1978年   1篇
  1977年   19篇
  1976年   48篇
  1968年   3篇
  1959年   1篇
  1957年   1篇
排序方式: 共有1325条查询结果,搜索用时 875 毫秒
31.
In a pilot study to establish fetal nucleated red blood cell (NRBC) detection in maternal blood, trisomy 13 was diagnosed by FISH analysis at 11 weeks' gestation. The NRBCs were detected after a single-step ficoll density gradient enrichment. In blood samples taken both before and after CVS, 52 and 80 NRBCs, respectively, were found to be positive for fetal haemoglobin. In 47 per cent of these cells, FISH analysis for X and Y chromosomes confirmed the fetal sex. Moreover, 48 per cent of these NRBCs showed three fluorescent signals for a chromosome 13 probe, which confirmed the diagnosis of trisomy 13, previously detected at CVS karyotyping. This is the first report of non-invasive prenatal diagnosis of trisomy 13, i.e., pre-CVS, in the first trimester. The high number of fetal NRBCs detected indicates a connection with aneuploidy, probably due to early impairment of the feto-maternal barrier.  相似文献   
32.
N-acetyltransferase (NAT) activity was determined by incubation of purified Enterobacter aerogenes enzyme with 2-aminofluorene (2-AF) as the substrate, followed by high pressure liquid chromatography assays. The NAT activity from E. aerogenes was 0.58 +/- 0.08 nmol/min/mg protein for 2-AF. The values of apparent K(m) and Vmax were 0.72 +/- 0.14 mM and 2.45 +/- 0.29 nmol/min/mg protein, respectively, for 2-AF. The optimal pH value for the enzyme activity was 7.5 for the 2-AF tested. The optimal temperature for enzyme activity was 37 degrees C for the 2-AF substrate. The molecular weight of NAT from E. aerogenes was 44.9 kD. Among a series of divalent cations and salts, Zn2+, Ca2+, and Fe2+ were demonstrated to be the most potent protease inhibitors, and only ethylenediaminetetraacetic acid significantly protected the NAT. Iodoacetamide, in contrast to other agents, markedly inhibited NAT.  相似文献   
33.
The newly developed antihypertensive drugs, the long-acting beta-blocker propranolol and the sustained release calcium antagonist verapamil, are compared in their antihypertensive, platelet function, rheological properties and metabolic effects. The trial was a double-blind, randomised, placebo-controlled cross-over study. Thirty patients with mild to moderate hypertension received propranolol (40-120 mg) or verapamil (80-200 mg) once daily in two separate ten week courses. After ten weeks treatment both drugs had significantly reduced both SBP and DBP. Beta-thromboglobulin (beta-TG) concentration, reflecting the status of platelet activation in vivo, was significantly decreased after propranolol (129.6 +/- 13.5 vs. 77.9 +/- 8.6 ng/ml) and verapamil (129.6 +/- 13.5 vs. 90.7 +/- 10.1 ng/ml) treatments while platelet aggregation induced by ADP, collagen, arachidonic acid or adrenaline and the production of thromboxane B2 (TXB2), 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) and platelet cyclic 3'-5' adenosine monophosphate (C-AMP) concentration were not affected. Significant alterations in rheological parameters such as plasma and whole blood viscosity, fibrinogen level and red cell deformability were not found. Higher cholesterol and low-density lipoprotein-cholesterol (LDL-C) levels were observed after propranolol treatment but not in verapamil treatment. Side-effects were mild, tolerated and no patient had to be withdrawn from the study. In conclusion, propranolol and verapamil are generally effective antihypertensive as well as rheologically safe drugs. Compared with the metabolic effect on serum lipid, verapamil may be a better choice. Both drugs possess the tendency to inhibit platelet properties which is desirable in hypertension treatment.  相似文献   
34.
A number of North American vegetable and animal fat shortenings, which had been analyzed previously for their physical and textural characteristics, were analyzed also for their chemical composition. The fatty acid and triglyceride composition of the solids were calculated by analyzing the composition of the original product and the liquid phase, and by determination of the solid fat content (SFC) of the fat. The solids were also isolated by isopropanol (IP) separation, and the high melting glycerides (HMG) by acetone crystallization at 15°C. There was not much difference in total saturates andtrans content between vegetable and animal fat shortenings. Changing formulations from soy-palm to soy-cottonseed does not change the total saturates plustrans content. The solids of the vegetable shortenings in the β form contained about 20% of 16:0, those in the β′ form 30% or more. The animal fat shortenings were mainly in the β form, their solids contained 30% or more of 16:0. C54 triglyceride content of the solids of β vegetable shortenings (calculated and IP-separated) was >45%, that of all animal fats was <25%. Solids of animal fat shortenings contain high levels of C52. The C54 triglycerides are β-tending and should be kept low in vegetable shortening. In the HMG the C54 should not exceed 30%. This can only be achieved by incorporation of a β′ hard fat, preferably palm hard fat. Animal fat, especially lard, crystallizes in the β form because the palmitic acid in the glyceride molecule is located in the 2-position, whereas those of vegetable fats are in the 1- and 3-position.  相似文献   
35.
36.
In July 1996, Tennessee initiated a managed mental health and substance abuse program called TennCare Partners. This publicly funded "carve-out" experiment started chaotically and soon deteriorated into a crisis. Many patients did not receive care or lost continuity of care, and the traditional "safety net" mental health system nearly disintegrated. This qualitative case study sought to ascertain the impact of the TennCare Partners program. It points out that the program's difficulties stemmed directly from a flawed design that spread funds previously earmarked for severely mentally ill patients across the entire Medicaid population. States contemplating similar reforms should strive to protect vulnerable patients by risk-adjusting capitation payments and by focusing resources on care for severely mentally ill persons. States should also minimize program complexity and ensure the accountability of managed care networks for their patients' behavioral health care needs.  相似文献   
37.
This paper deals with the problem of exponential stability for a class of linear discrete switched systems with constant delays.The switched systems consist of stable and unstable subsystems.Based on the average dwell time method, some switching signals will be found to guarantee exponential stability of these systems.The explicit state decay estimation is also given in the form of the solutions of linear matrix inequalities(LMIs).An example relating to networked control systems(NCSs) illustrates the effect...  相似文献   
38.
It is not generally appreciated that pseudoxanthoma elasticum (PXE) can be associated with epidermal perforation by elastic fibers. We report an example of this phenomenon. The term "perforating PXE" is suggested and a distinction is made from elastosis perforans serpiginosa (EPS). We believe that most reported cases of coexistence of PXE and EPS are perforating PXE and that the coexistence of EPS has not been clearly demonstrated.  相似文献   
39.
40.
A review of the various models of New Product Development (NPD) process shows that although different approaches have been proposed, they are in fact all variants on a linear theme: some may include feedback loops, but they all essentially advocate that certain steps precede, or are preceded by, others. An inevitable consequence on the Internet/World Wide Web (WWW or Web) is that such models are no longer applicable. Based on the lessons learned from the development of a new financial service offered via the Internet, we show how such assumptions of linearity need no longer be a constraint. In addition, innovativeness is not related to firm size. But the fact that the Web allows for the real-time development of new financial services based on on-going feedback from potential and current customers raises a new set of managerial issues that have to be tackled. The objective of this paper is to use the context of the recent launch of an innovative financial service product via the Web to explore the managerial changes that are starting to affect the banking industry.  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