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   3156篇
  免费   7篇
  国内免费   1篇
综合类   2篇
化学工业   32篇
金属工艺   11篇
机械仪表   13篇
建筑科学   6篇
能源动力   13篇
轻工业   13篇
水利工程   5篇
石油天然气   3篇
无线电   10篇
一般工业技术   24篇
冶金工业   3017篇
原子能技术   2篇
自动化技术   13篇
  2022年   4篇
  2021年   2篇
  2020年   2篇
  2019年   3篇
  2018年   4篇
  2017年   3篇
  2016年   5篇
  2014年   9篇
  2013年   14篇
  2012年   7篇
  2011年   5篇
  2010年   12篇
  2009年   7篇
  2008年   3篇
  2007年   9篇
  2006年   4篇
  2005年   4篇
  2004年   4篇
  2003年   6篇
  2002年   9篇
  2001年   4篇
  2000年   4篇
  1999年   92篇
  1998年   839篇
  1997年   460篇
  1996年   295篇
  1995年   187篇
  1994年   127篇
  1993年   204篇
  1992年   34篇
  1991年   41篇
  1990年   38篇
  1989年   54篇
  1988年   45篇
  1987年   47篇
  1986年   46篇
  1985年   49篇
  1984年   2篇
  1983年   6篇
  1982年   13篇
  1981年   34篇
  1980年   32篇
  1979年   2篇
  1978年   7篇
  1977年   106篇
  1976年   249篇
  1975年   14篇
  1971年   2篇
  1955年   4篇
  1930年   1篇
排序方式: 共有3164条查询结果,搜索用时 14 毫秒
61.
The concentrations of the soluble adhesion molecules E-cadherin, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were investigated in 45 patients with gastric cancer before treatment and their correlation with clinical, histological and routine laboratory parameters was examined. Data were collected on tumour stage at presentation, presence and sites of metastatic disease, tumour pathology, survival and results of routine laboratory tests. Serum concentrations of ICAM-1 and VCAM-1 were significantly elevated in the patients with gastric cancer in comparison with the group of healthy subjects (P < 0.00001 and P < 0.0001 respectively). Increased serum concentrations of VCAM-1 were associated with locally advanced and metastatic disease whereas ICAM-1 was significantly elevated both in local and in advanced/metastatic disease. Soluble E-cadherin and E-selectin concentrations did not show any significant elevation in gastric cancer patients. Concentrations of soluble adhesion molecules showed significant correlation with each other (except E-selectin and VCAM-1) and with alkaline phosphatase. Soluble ICAM-1 and VCAM-1 were significantly associated with an elevated total white cell count. Patients with elevated VCAM-1 had significantly poorer survival in comparison with patients with normal serum levels (P = 0.0361).  相似文献   
62.
The treatment of alcoholism has changed during the past 2 decades. Notable developments have occurred in pharmacotherapy, psychotherapy, and health-care delivery. A better understanding of the biologic basis for addiction has led to clinical trials of medications that target neuroreceptors. One such medication is the opiate antagonist naltrexone, which decreases the craving for alcohol. Psychosocial interventions continue to be the mainstay of alcohol treatment programs. The efficacy of three different therapies was demonstrated in a study called Project MATCH (Matching Alcoholism Treatments to Client Heterogeneity). This study, however, did not prove the patient-treatment "matching" hypothesis. In addition to therapies provided by addiction specialists, interest is growing in the use of brief motivational techniques in primary-care settings. As the field of addiction responds to an unfolding health-care delivery system, a broader range of treatment options in conjunction with a greater opportunity to individualize patient care is evolving.  相似文献   
63.
The polycyclic aromatic hydrocarbon (PAH), chrysene, was linked to the solid support TentaGel S-NH2 via a linker by means of synthesis. The resulting product 4-(chrysene-1-yloxy)-N-(TentaGel S)butanamide (4) was then evaluated for its ability to isolate PAHs from solution by means of π-π-interactions.  相似文献   
64.
The thermo-oxidative behavior of unformulated (unfilled) samples of epoxy coatings has been studied at five temperatures ranging from 70 °C to 150 °C. Two epoxy networks based on diglycidyl ether of bisphenol A (DGEBA), respectively, cured by jeffamine (POPA) or polyamidoamine (PAA) were compared. Infrared spectrophotometry (IR), differential scanning (DSC) and sol–gel analysis (SGA) were used to monitor structural changes.  相似文献   
65.
为了获得性能优良的耐热镁合金,研究了Sr对初生和共晶Mg_2Si相的变质作用,并利用扫描电子显微镜观察了Mg_2Si相的形貌特征与Mg-1.7Si-x Sr合金的微观组织.结果表明,当Sr的质量分数处于1.0%~1.5%范围内时,可对初生和共晶Mg_2Si相进行有效变质.Sr的吸附作用可以诱发孪晶沟槽、旋转晶界等原子扩展台阶的出现,引起原子堆砌方式和晶体生长方向的改变,因而Sr可对初生Mg_2Si相起到变质作用.Sr的添加还可将Mg+Mg_2Si共晶的长大方式由合作长大模式变为以重新形核为主兼有合作长大的混合模式,使得Mg_2Si相的生长形态产生改变,因而Sr可对共晶Mg_2Si起到变质作用.  相似文献   
66.
Membranes from the gill cilia of the mollusc Aequipecten irradians may be solubilized readily with Nonidet P-40. When the detergent is removed from the solution by adsorption to polystyrene beads, the proteins of the extract remain soluble. However, when the solution is frozen and thawed, nearly all of the proteins reassociate to form membrane vesicles, recruiting lipids from the medium. The membranes equilibrate as a narrow band (d = 1.167 g/cm3) upon sucrose density gradient centrifugation. The lipid composition of reconstituted membranes (1:2 cholesterol:phospholipids) closely resembles that of the original extract, as does the protein content (45%). Ciliary calmodulin is the major extract protein that does not associate with the reconstituted membrane, even in the presence of 1 mM calcium ions, suggesting that it is a soluble matrix component. The major protein of reconstituted vesicles is membrane tubulin, shown previously to differ hydrophobically from axonemal tubulin. The tubulin is tightly associated with the membrane since extraction with 1 mM iodide or thiocyanate leaves a vesicle fraction whose protein composition and bouyant density are unchanged. Subjecting the detergent-free membrane extract to a freeze-thaw cycle in the presence of elasmobranch brain tubulin or forming membranes by warming the extract in the presence of polymerization-competent tubulin yields a membrane fraction with little incorporated brain tubulin. This suggests that ciliary membrane tubulin specifically associates with lipids, whereas brain tubulin preferentially forms microtubules.  相似文献   
67.
We present a search space analysis and its application in improving local search algorithms for the graph coloring problem. Using a classical distance measure between colorings, we introduce the following clustering hypothesis: the high quality solutions are not randomly scattered in the search space, but rather grouped in clusters within spheres of specific diameter. We first provide intuitive evidence for this hypothesis by presenting a projection of a large set of local minima in the 3D space. An experimental confirmation is also presented: we introduce two algorithms that exploit the hypothesis by guiding an underlying Tabu Search (TS) process. The first algorithm (TS-Div) uses a learning process to guide the basic TS process toward as-yet-unvisited spheres. The second algorithm (TS-Int) makes deep investigations within a bounded region by organizing it as a tree-like structure of connected spheres. We experimentally demonstrate that if such a region contains a global optimum, TS-Int does not fail in eventually finding it. This pair of algorithms significantly outperforms the underlying basic TS algorithm; it can even improve some of the best-known solutions ever reported in the literature (e.g. for dsjc1000.9).  相似文献   
68.
Many enteroviruses, members of the family Picornaviridae, cause a rapid and drastic inhibition of host cell protein synthesis during infection, a process referred to as host cell shutoff. Poliovirus, one of the best-studied enteroviruses, causes marked inhibition of host cell translation while preferentially allowing translation of its own genomic mRNA. An abundance of experimental evidence has accumulated to indicate that cleavage of an essential translation initiation factor, eIF4G, during infection is responsible at least in part for this shutoff. However, evidence from inhibitors of viral replication suggests that an additional event is necessary for the complete translational shutoff observed during productive infection. This report examines the effect of poliovirus infection on a recently characterized 3' end translational stimulatory protein, poly(A)-binding protein (PABP). PABP is involved in stimulating translation initiation in lower eukaryotes by its interaction with the poly(A) tail on mRNAs and has been proposed to facilitate 5'-end-3'-end interactions in the context of the closed-loop translational model. Here, we show that PABP is specifically degraded during poliovirus infection and that it is cleaved in vitro by both poliovirus 2A and 3C proteases and coxsackievirus B3 2A protease. Further, PABP cleavage by 2A protease is accompanied by concurrent loss of translational activity in an in vitro-translation assay. Similar loss of translational activity also occurs simultaneously with partial 3C protease-mediated cleavage of PABP in translation assays. Further, PABP is not degraded during infections in the presence of guanidine-HCl, which blocks the complete development of host translation shutoff. These results provide preliminary evidence that cleavage of PABP may contribute to inhibition of host translation in infected HeLa cells, and they are consistent with the hypothesis that PABP plays a role in facilitating translation initiation in higher eukaryotes.  相似文献   
69.
70.
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