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   9853篇
  免费   24篇
  国内免费   1篇
电工技术   21篇
综合类   6篇
化学工业   281篇
金属工艺   31篇
机械仪表   13篇
建筑科学   36篇
矿业工程   1篇
能源动力   14篇
轻工业   79篇
水利工程   14篇
石油天然气   3篇
武器工业   1篇
无线电   113篇
一般工业技术   186篇
冶金工业   8901篇
原子能技术   9篇
自动化技术   169篇
  2020年   14篇
  2018年   15篇
  2015年   13篇
  2014年   16篇
  2013年   48篇
  2012年   37篇
  2011年   50篇
  2010年   30篇
  2009年   32篇
  2008年   37篇
  2007年   55篇
  2006年   35篇
  2005年   34篇
  2004年   30篇
  2003年   42篇
  2002年   26篇
  2001年   31篇
  2000年   32篇
  1999年   311篇
  1998年   2796篇
  1997年   1582篇
  1996年   1008篇
  1995年   586篇
  1994年   465篇
  1993年   570篇
  1992年   85篇
  1991年   117篇
  1990年   109篇
  1989年   102篇
  1988年   111篇
  1987年   105篇
  1986年   105篇
  1985年   79篇
  1984年   17篇
  1983年   22篇
  1982年   53篇
  1981年   55篇
  1980年   90篇
  1979年   14篇
  1978年   26篇
  1977年   205篇
  1976年   477篇
  1975年   21篇
  1974年   16篇
  1973年   13篇
  1972年   16篇
  1971年   14篇
  1970年   13篇
  1969年   19篇
  1968年   13篇
排序方式: 共有9878条查询结果,搜索用时 62 毫秒
991.
The characteristics of the five Korean isolates of Japanese encephalitis (JE) virus were compared with those of the already reported JE virus strains from Japan and China using the hemagglutination test and polymerase chain reaction direct sequencing of the JE virus genomes (capsid/premembrane, envelope region). The hemagglutination patterns of all the isolates were distinctly different from the Nakayama-NIH strain. The optimal pH of hemagglutination of all the Korean isolates was 6.6-7.0 and the reaction range was broader than that of the Nakayama-NIH strain. The 198 nucleotide sequences in the capsid/premembrane gene region of the five Korean strains indicated that they were classified into the third genotype group, the JE strains from the countries in the temperate zone including the Nakayama-NIH, JaOArS982, and Beijing-1 strains. Four of the five Korean isolates formed a unique phylogenetic tree within the third genotype group, although the last one was genetically highly related to the Nakayama-NIH strain. The 251 nucleotide sequences in the envelope region of the five isolates were more divergent than the capsid/premembrane region. Four of the five isolates showed a large nucleotide divergency as compared with the JaOArS982 strain (< or = 12.4%), but the last one was similar to the JaOArS982 strain (98% of nucleotide homology). These results suggest the evolutionary divergence of the JE viruses isolated in Korea from the Japanese and Chinese strains and that there may exist at least two antigenically different JE virus strains in Korea.  相似文献   
992.
In contrast with cross-sectional designs used in previous studies, this exploratory study compared survey data from 127 matched pairs of clinical pharmacists and physicians working together. Physicians' perceptions of the importance of clinical pharmacy activities for patient care and the competence of pharmacists performing the activities were examined for their influence on prescribing behavior in an institutional setting. Data from a national survey showed that physicians rated pharmacists higher regarding recommendations based on drug use evaluations (p = 0.004) and competency to provide all clinical pharmacy services. Scores for pharmacokinetics ratings were similar between pharmacists and physicians (p = 0.168). Pharmacists rated the importance of recommendations based on cost-effectiveness higher than physicians (p = 0.012). Overall, physicians' perceptions of activity importance for patient care and pharmacist competency appear to dictate pharmacists' influence on physician prescribing behavior (R = 0.723).  相似文献   
993.
Cyclosporine was introduced in 1981 as an immunosuppressive agent in renal transplantation. Its use was soon extended to the treatment of various glomerular disorders. In light of its known immunomodulating effects, the use of cyclosporine has been most prominent in those glomerular diseases thought to have an immune basis. The most careful studies of cyclosporine in glomerular diseases have been performed in the pediatric population with idiopathic nephrotic syndrome (i.e., minimal change disease and focal segmental glomerulosclerosis), although data are accumulating regarding efficacy and safety in adults with idiopathic nephrotic syndrome. In patients who are steroid-dependent, cyclosporine therapy can induce complete or partial remission in a significant proportion of cases; success rates in patients with steroid-resistant nephrotic syndrome are less encouraging. Treatment with cyclosporine allows for dose reduction or elimination of corticosteroids, and the consequent salutary effect on growth in the child and glucose and bone metabolism in all patients. Studies that suggest a potential benefit of cyclosporine in recurrent nephrotic syndrome in renal allografts and in other glomerular diseases are also discussed.  相似文献   
994.
Emerging emphases on systems of care, cost containment, and preventive interventions require the CNS to recognize risk factors and change health behaviors before complications develop. To lower substantially the rate of nontraumatic lower extremity amputation, high-risk populations must be screened and must receive appropriate management, including education and self-care interventions. In this article, two studies that examined foot risk factors in ambulatory elderly with intact feet are compared. American Diabetes Association and Gillis W. Long Hansen's Disease Center risk criteria were applied to both datasets. Recommendations for education, management, and referrals based on the calculated level of risk are presented.  相似文献   
995.
Benzoporphyrin derivative (BPD), a sensitizer currently in clinical trials, was evaluated for the treatment of experimental Greene melanoma implanted in the rabbit iris. To improve tumor targeting, BPD was complexed with low-density lipoprotein (LDL) representing an endogenous carrier system for BPD as previously described. Twelve tumors were irradiated at a sensitizer dose of 2 mg kg-1 body weight using a dye laser at 692 nm. Tumor responses were documented by photography, angiography and light and electron microscopy. All tumors treated with 80 J cm-2 regressed irreversibly. The principal mechanism of tumor necrosis was thrombosis following disruption of endothelial membranes. Ultrastructure data suggested tumor cell damage, although evidence for this being the result of direct PDT-mediated tumor cell death was less clear. These data suggest that BPD-LDL may be used to improve the selectivity of photodynamic tumor therapy possibly by the increased uptake of lipoprotein-delivered sensitizer to neovascular endothelial cells.  相似文献   
996.
Dysfunctions in serotonergic pathways may underlie several psychiatric disorders. The reuptake of serotonin (5-HT) from synaptic terminals is mediated by a specific transporter (5-HTT). Genetic variation in the gene coding for the 5-HTT protein might be involved in the predisposition to psychiatric disorders. A systematic screening of the whole coding sequence of the 5-HTT gene in mood disorder (MD) and obsessive-compulsive disorder (OCD) patients, as well as in healthy controls, using PCR and denaturing gradient gel electrophoresis (DGGE) revealed the presence of two mutations. The first was in intron 4, and the second was a C-->A transversion leading to an amino-acid exchange (Leu-->Met) in position 255 of the deduced protein sequence. No further occurrence of this substitution was found in an extended sample of patients and controls. Therefore, structural modifications of the 5-HTT gene do not seem to play either a major or minor role in the genetic predisposition to MD or OCD.  相似文献   
997.
RNA tertiary structure mediation by adenosine platforms   总被引:4,自引:0,他引:4  
The crystal structure of a group I intron domain reveals an unexpected motif that mediates both intra- and intermolecular interactions. At three separate locations in the 160-nucleotide domain, adjacent adenosines in the sequence lie side-by-side and form a pseudo-base pair within a helix. This adenosine platform opens the minor groove for base stacking or base pairing with nucleotides from a noncontiguous RNA strand. The platform motif has a distinctive chemical modification signature that may enable its detection in other structured RNAs. The ability of this motif to facilitate higher order folding provides one explanation for the abundance of adenosine residues in internal loops of many RNAs.  相似文献   
998.
999.
Aspirin has an established benefit in reducing the incidence of coronary events and vein graft occlusion. We have now assessed the risk of pre-operative aspirin in a prospective, randomised, double-blind clinical trial in 100 patients scheduled for elective coronary artery surgery. Any prescribed aspirin and non-steroidal anti-inflammatory drugs were discontinued 2 weeks pre-operatively and these were replaced by a randomly assigned tablet of either aspirin 300 mg daily or placebo taken until the day of surgery. Patient compliance was confirmed by serum and urinary salicylate analysis. The two groups were similar in demographic characteristics, bypass time, number of grafts placed and number of internal mammary arteries used. All patients survived to be discharged home (see Table). Aspirin decreases platelet aggregation to arachidonic acid and to collagen both pre- and post-operatively. The benefit of pre-operative aspirin has to be balanced against the risk of increasing post-operative blood loss, re-exploration for excessive bleeding and transfusion requirements.  相似文献   
1000.
The fracture callus contribution to the total rigidity of external fixator-fractured bone element was analysed. This study was achieved from both theoretical and experimental perspectives. The theoretical study was done using the finite element method with a three-dimensional model. In this model, both the callus and the development of its elastic characteristics were considered. A series of 38 New Zealand-California white rabbits with tibial fractures treated with some external fixation system was used in this study. Such devices could reproduce either rigid or elastic features. The frame dynamization can be obtained at different fracture healing stages. Animals were classified into four series: (1) rigid fixators, (2) dynamized fixators two weeks after surgery, (3) three weeks after surgery and (4) four weeks after surgery. Tension tests were performed to evaluate callus strength. Theoretical results showed significant levels of callus load transmission (85.5%) when the callus elastic modulus is 1/100 of the elastic modulus of intact bone in an external fixator with rigid features. Experimental analysis of the callus obtained with different external fixator systems did not show differences among them. This fact implies that the immature callus theoretically modelled (E = 100 N mm-2) appears early in the rabbit fracture model (before two weeks, when first dynamization was made), for this reason no differences were found between the two types of treatment (rigid and dynamized systems). This fact questions the reliability of the dynamization process in external fixation of fractures and it implies accurate investigations in the clinical field.  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