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   7414篇
  免费   172篇
  国内免费   8篇
电工技术   81篇
综合类   2篇
化学工业   1327篇
金属工艺   135篇
机械仪表   119篇
建筑科学   361篇
矿业工程   6篇
能源动力   146篇
轻工业   505篇
水利工程   46篇
石油天然气   14篇
武器工业   2篇
无线电   383篇
一般工业技术   994篇
冶金工业   2353篇
原子能技术   45篇
自动化技术   1075篇
  2022年   55篇
  2021年   77篇
  2020年   62篇
  2019年   95篇
  2018年   92篇
  2017年   79篇
  2016年   98篇
  2015年   103篇
  2014年   137篇
  2013年   359篇
  2012年   238篇
  2011年   337篇
  2010年   272篇
  2009年   246篇
  2008年   324篇
  2007年   279篇
  2006年   258篇
  2005年   200篇
  2004年   195篇
  2003年   178篇
  2002年   188篇
  2001年   99篇
  2000年   86篇
  1999年   131篇
  1998年   474篇
  1997年   303篇
  1996年   228篇
  1995年   181篇
  1994年   164篇
  1993年   173篇
  1992年   112篇
  1991年   90篇
  1990年   88篇
  1989年   114篇
  1988年   68篇
  1987年   78篇
  1986年   93篇
  1985年   107篇
  1984年   80篇
  1983年   97篇
  1982年   88篇
  1981年   95篇
  1980年   79篇
  1979年   79篇
  1978年   62篇
  1977年   88篇
  1976年   105篇
  1975年   67篇
  1974年   48篇
  1973年   53篇
排序方式: 共有7594条查询结果,搜索用时 0 毫秒
951.
This paper explores two dimensions of internalized object relations in borderline and schizophrenic patients using Rorschach scales. A thematic and a structural Rorschach measure of object relations is applied to the Rorschachs of two borderline groups (an infantile personality group and an obsessive-paranoid group) and a schizophrenic group. The findings suggest the value of both a multidimensional definition of internalized object relations and the use of such an approach to clarifying the diagnostic concept of borderline personality disorder. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
952.
953.
Parasitic third-stage larvae of the sheep abomasal nematode Haemonchus contortus develop and molt in vitro to the fourth stage (L4) in 48-72 hr, at which time they begin feeding. Coincident with the third molt, larvae begin to secrete significant amounts of protein into culture fluids, including a zinc metalloproteinase. This culture-derived zinc metalloproteinase differs from a previously described metalloproteinase from infective third-stage larvae (L3[2M]), which mediates the ecdysis process. These differences include time of expression, molecular mass, and substrate specificity. The purified proteinase, from cultures of L4, has a molecular weight of approximately 46 kDa, functions as an endopeptidase, and digests several native proteins of host origin including fibrinogen and fibronectin.  相似文献   
954.
The major inhibitory components obtained after fractionation of an aqueous extract of field-grown sorghum (Sorghumbicolorcv. Bird-a-boo) herbage were quantified in terms of biological potency by indexing three aspects of cumulative cress (Lepidium sativum cv. Curlycress) seed germination. The inhibitory potential expressed in the crude aqueous extract reflected a complex interaction of numerous individual components of diverse chemical compositions and potencies. Some of these inhibitory components included chemical classes not previously associated with herbage phytotoxicity.  相似文献   
955.
956.
Mutations at the phosphorylation site (Asp-378) of the yeast plasma-membrane H+-ATPase have been shown previously to cause misfolding of the ATPase, preventing normal movement along the secretory pathway; Asp-378 mutations also block the biogenesis of co-expressed wild-type ATPase and lead to a dominant lethal phenotype. To ask whether these defects are specific for Asp-378 or whether the phosphorylation region as a whole is involved, alanine-scanning mutagenesis has been carried out to examine the role of 11 conserved residues flanking Asp-378. In the sec6-4 expression system (Nakamoto, R. K., Rao, R., and Slayman, C. W. (1991) J. Biol. Chem. 266, 7940-7949), the mutant ATPases displayed varying abilities to reach the secretory vesicles that deliver plasma-membrane proteins to the cell surface. Indirect immunofluorescence of intact cells also gave evidence for a spectrum of behavior, ranging from mutant ATPases completely arrested (D378A, K379A, T380A, and T384A) or partially arrested in the endoplasmic reticulum to those that reached the plasma membrane in normal amounts (C376A, S377A, and G381A). Although the extent of ER retention varied among the mutants, the endoplasmic reticulum appeared to be the only secretory compartment in which the mutant ATPases accumulated. All of the mutant proteins that localized either partially or fully to the ER were also malfolded based on their abnormal sensitivity to trypsin. Among them, the severely affected mutants had a dominant lethal phenotype, and even the intermediate mutants caused a visible slowing of growth when co-expressed with wild-type ATPase. The effects on growth could be traced to the trapping of the wild-type enzyme with the mutant enzyme in the ER, as visualized by double label immunofluorescence. Taken together, the results indicate that the residues surrounding Asp-378 are critically important for ATPase maturation and transport to the cell surface.  相似文献   
957.
Adherence of Haemophilus influenzae to epithelial cells plays a central role in colonization and is the first step in infection with this organism. Pili, which are large polymorphic surface proteins, have been shown to mediate the binding of H. influenzae to cells of the human respiratory tract. Earlier experiments have demonstrated that the major epitopes of H. influenzae pili are highly conformational and immunologically heterogenous; their subunit pilins are, however, immunologically homogenous. To define the extent of structural variation in pilins, which polymerize to form pili, the pilin genes (hifA) of 26 type a to f and 16 nontypeable strains of H. influenzae were amplified by PCR and subjected to restriction fragment length polymorphism (RFLP) analysis with AluI and RsaI. Six different RFLP patterns were identified. Four further RFLP patterns were identified from published hifA sequences from five nontypeable H. influenzae strains. Two patterns contained only nontypeable isolates; one of these contained H. influenzae biotype aegyptius strains F3031 and F3037. Another pattern contained predominantly H. influenzae type f strains. All other patterns were displayed by a variety of capsular and noncapsular types. Sequence analysis of selected hifA genes confirmed the 10 RFLP patterns and showed strong identity among representatives displaying the same RFLP patterns. In addition, the immunologic reactivity of pili with antipilus antisera correlated with the groupings of strains based on hifA RFLP patterns. Those strains that show greater reactivity with antiserum directed against H. influenzae type b strain M43 pili tend to fall into one RFLP pattern (pattern 3); while those strains that show equal or greater reactivity with antiserum directed against H. influenzae type b strain Eagan pili tend to fall in a different RFLP pattern (pattern 1). Sequence analysis of representative HifA pilins from typeable and nontypeable H. influenzae identified several highly conserved regions that play a role in bacterial pilus assembly and other regions with considerable amino acid heterogeneity. These regions of HifA amino acid sequence heterogeneity may explain the immunologic diversity seen in intact pili.  相似文献   
958.
959.
We develop two applications of middle-out reasoning in inductive proofs: logic program synthesis and the selection of induction schemes. Middle-out reasoning as part of proof planning was first suggested by Bundy et al. Middle-out reasoning uses variables to represent unknown terms and formulae. Unification instantiates the variables in the subsequent planning, while proof planning provides the necessary search control. Middle-out reasoning is used for synthesis by planning the verification of an unknown logic program: The program body is represented with a meta-variable. The planning results both in an instantiation of the program body and a plan for the verification of that program. If the plan executes successfully, the synthesized program is partially correct and complete. Middle-out reasoning is also used to select induction schemes. Finding an appropriate induction scheme during synthesis is difficult because the recursion of the program, which is unknown at the outset, determines the induction in the proof. In middle-out induction, we set up a schematic step case by representing the constructors that are applied to induction variables with meta-variables. Once the step case is complete, the instantiated variables correspond to an induction appropriate to the recursion of the program. We have implemented these techniques as an extension of the proof planning system CL A M, called Periwinkle, and synthesized a variaety of programs fully automatically. Supported by the Swiss National Science Foundation and ARC Project BC/DAAD Grant 438. The work described in this paper was carried out while the first author was at the Department of Artificial Intelligence of the University of Edinburgh. Supported by the German Ministry for Research and Technology (BMFT) under grant ITS 9102 and ARC Project BC/DAAD Grant 438. Responsibility for the contents of this publication lies with the authors. Supported by SERC grant GR/J/80702, ESPRIT BRP grant 6810, ESPRIT BRP grant EC-US 019-76094, and ARC Project BC/DAAD Grant 438.  相似文献   
960.
An efficient monoclonal aldolase antibody that proceeds by an enamine mechanism was generated by reactive immunization. Here, this catalyst has been used in the total synthesis of epothilones A (1) and C (3). The starting materials for the synthesis of these molecules have been obtained by using antibody-catalyzed aldol and retro-aldol reactions. These precursors were then converted to epothilones A (1) and C (3) to complete the total synthesis.  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