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   318019篇
  免费   3482篇
  国内免费   1295篇
电工技术   6611篇
综合类   341篇
化学工业   44930篇
金属工艺   17159篇
机械仪表   12934篇
建筑科学   7595篇
矿业工程   1262篇
能源动力   6924篇
轻工业   25262篇
水利工程   2950篇
石油天然气   2854篇
武器工业   3篇
无线电   38088篇
一般工业技术   64438篇
冶金工业   55989篇
原子能技术   4927篇
自动化技术   30529篇
  2021年   1563篇
  2019年   1424篇
  2018年   11009篇
  2017年   11603篇
  2016年   7248篇
  2015年   2457篇
  2014年   3248篇
  2013年   10847篇
  2012年   8125篇
  2011年   16343篇
  2010年   14467篇
  2009年   13982篇
  2008年   14195篇
  2007年   16369篇
  2006年   7107篇
  2005年   10245篇
  2004年   8257篇
  2003年   7878篇
  2002年   6874篇
  2001年   6434篇
  2000年   5927篇
  1999年   6437篇
  1998年   16563篇
  1997年   11598篇
  1996年   8960篇
  1995年   6699篇
  1994年   5934篇
  1993年   5750篇
  1992年   4066篇
  1991年   4016篇
  1990年   3582篇
  1989年   3504篇
  1988年   3447篇
  1987年   2907篇
  1986年   2842篇
  1985年   3413篇
  1984年   3050篇
  1983年   2743篇
  1982年   2547篇
  1981年   2568篇
  1980年   2430篇
  1979年   2271篇
  1978年   2235篇
  1977年   2808篇
  1976年   4171篇
  1975年   1899篇
  1974年   1795篇
  1973年   1783篇
  1972年   1460篇
  1971年   1317篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A cDNA encoding a new type of alcohol dehydrogenase was cloned from a human stomach cDNA library. PCR amplification of 5'-stretch human stomach lambda gt11 library, using degenerate inosine-containing oligonucleotide probes compatible with peptide sequences of human sigma-ADH, resulted in a single product. Subsequently, internal non-degenerate primers were constructed according to the sequences occurring in the product. By PCR with combinations of these new primers and lambda gt11 forward and reverse primers, fragments of the cDNA containing its 5' and 3' ends were amplified. The full length cDNA sequence has 1125 nucleotides with a 72% similarity to those of human class I ADH. The polypeptide sequence, predicted from the cDNA, corresponds to 373 amino acids with a high degree of similarity (96%) to fragments of sigma-ADH previously reported. Northern hybridization analysis with the specific probe for the mRNA of this protein showed that it is expressed in the human stomach but not in the liver. These data indicate that the cDNA we cloned is that of human class IV ADH.  相似文献   
992.
993.
Insulin-dependent diabetes mellitus (IDDM) is a T-cell-mediated autoimmune disease whose onset is believed to be triggered by unknown environmental factors acting on a predisposing genetic background. Islet-infiltrating T (IIT) cells from two IDDM patients, who had died at the onset of the disease from brain swelling as a complication of ketoacidosis, were analysed. The results provided evidence for the involvement of a pancreatic islet cell membrane-bound superantigen as a diabetes aetiopathogenetic factor. There was a selective expansion of a T-cell receptor (TCR) variable segment of the beta-chain (V beta 7) in these IIT cells in association with unselected V alpha-chain segments; extensive junctional diversity of the TCR V beta 7 chains; and evidence of positive selection, after exposure to diabetic islet cell membrane preparations, of V beta 7+ T-cell clones among peripheral blood lymphocytes from non-diabetic individuals.  相似文献   
994.
OBJECTIVE: To better understand the immunoglobulin variable (V) region repertoire of rheumatoid factors (RF). METHODS: We characterized the heavy (H) and light (L) chain gene segments utilized in a monospecific IgG RF secreting hybridoma (AEE111F) which were derived from a patient with rheumatoid arthritis (RA). The hybridoma was established by fusion of a mouse myeloma cell line with bone marrow derived mononuclear cells from a patient with RA. First strand complementary DNA (cDNA) was generated and used for a polymerase chain reaction amplification of the H and L chain V domains. The amplified V domains were sequenced and compared with an extensive database of germline and cDNA V gene segments. RESULTS: The VH sequence was found to be 96% homologous to a previously described fetal VH3 cDNA (60P2). The VL sequence was also highly homologous to the previously described V lambda II gene (96%) derived from a patient with systemic lupus erythematosus which correlated with an 8.12 idiotype (Id), and to an antibacterial antibody against the Haemophilus influenzae type b capsular polysaccharide (94.7%). CONCLUSION: The overlap among this RF VL gene and the 2 reported V lambda sequences of antibodies that expressed anti-DNA related Id and an environmental pathogen specificity suggests that a part of the IgG RF isolated from patients with RA may thus be derived from the physiological natural antibody repertoire during an abnormal immune response and then develop high affinity, monospecific RF by the selection of an antigen driven mechanism.  相似文献   
995.
996.
A survey of perceptions of IS personnel – managers, technical specialists and programmer/analysts – was conducted by the Association for Technical Information in Spain, using the JDS/DP, a modification of the job diagnostic survey instrument. Data were collected on fifteen job variables, related to four motivation aspects: job components, satisfaction levels, need for growth/achievement and goal participation/feedback. The results were compared with those of a similar survey for the same job types in Finland. Results were also compared with the norms developed for computer personnel in the USA. The survey revealed that personnel attracted to the computer field have a high need for growth and a low need for social interaction. It also revealed that the work itself was ranked highest among eleven motivating factors. For both Spain and Finland, the technical specialist job had a mis-match between the job's motivating potential and the employee's need for growth, compared with similar personnel in the USA. By examining the core job dimensions, managers can redesign the job to produce a match between these two major components of motivation.  相似文献   
997.
A 59-year-old female patient with atypical chronic herpes simplex encephalitis was reported. Initial symptom was persistent myoclonus involving the trunk and limb muscles, and later lateral gaze palsy to the left side, cerebellar ataxia, consciousness disturbance and other brainstem symptoms including absence of corneal and gag reflex and vocal cord palsy developed. The patient was successfully treated with high dose of acyclovir. Electroencephalogram was normal in the initial stage but later showed diffuse slow waves. Although CT scan and MRI showed no abnormal finding in the cerebral cortex, brainstem lesion was observed on PD weighted image of MRI. Lumbar puncture yielded a clear cerebrospinal fluid, with slightly elevated protein, increased lymphocytes, and elevated titer of herpes simplex virus type I. The serological data, albumin ratio (10.3), antibody index (12.3) and antibody ratio (7.1) were consistent with herpes simplex encephalitis. Ten days' administration of acyclovir, 1,200 mg a day and repeated three times, was prominently effective for the myoclonus and consciousness disturbance. A diagnosis of chronic herpes simplex encephalitis initially presenting with brainstem encephalitis was made. Judging from the clinical and EEG findings, the brainstem lesion was initially thought to be a cause of myoclonus in this case. However, somatosensory evoked potential (SPE) of both upper and lower extremities revealed enlarged amplitude (giant SEP), and long loop reflex was enhanced (C-reflex) on the left. Giant SEP and C-reflex imply cerebral cortex as the origin of the myoclonus. Brainstem inflammatory lesion might have involved the ascending inhibitory system, thus disinhibiting the cortical sensorimotor area and causing cortical myoclonus.  相似文献   
998.
AM-1155 is a newly synthesized 6-fluoro-8-methoxy quinolone. We assessed its in vitro antimycobacterial activity using sparfloxacin (SPFX) and ofloxacin (OFLX) as comparison drugs. The MICs of these agents for various mycobacterial strains were determined by the agar dilution method with 7H11 medium. AM-1155 had lower MICs for 50 and 90% of tested strains of Mycobacterium kansasii, M. marinum, and M. fortuitum-M. chelonae complex than SPFX and OFLX, and the values for M. tuberculosis, M. scrofulaceum, and the M. avium-M. intracellulare complex were similar to those of SPFX and considerably lower than those of OFLX. In addition, the antimicrobial activity of AM-1155 against M. tuberculosis and M. intracellulare phagocytosed into murine peritoneal macrophages was compared with that of OFLX. AM-1155 (1 microgram/ml) inhibited the intracellular growth of both M. tuberculosis and M. intracellulare, whereas OFLX at the same concentration failed to show any such effect. Moreover, AM-1155 (10 micrograms/ml) exhibited a steady bactericidal action against M. tuberculosis, whereas OFLX at the same concentration had only a weak effect. AM-1155 (10 micrograms/ml) also inhibited the growth of M. intracellulare more effectively than OFLX.  相似文献   
999.
In this paper the results are presented of a test program on the energy absorption of composite cylinders loaded in compression. The influence of the laminate lay-up and of the trigger configuration were determined. Two different failure modes for the different laminates and triggers were observed: a splaying mode and a fragmentation mode. The splaying mode is more efficient in absorbing energy. The failure mode did not change during the crushing process.  相似文献   
1000.
A new multiaxial fatigue damage model for orthotropic materials is proposed based on the strain vector. Six material constants are included in the model. These material constants represent the dependence of fatigue resistance on material orientation, and they can be obtained by conducting strain-controlled uniaxial fatigue tests along the three principal orthotropic directions of an orthotropic material. The model can also be transformed in new coordinate systems to predict the fatigue lives of new material orientations. Biaxial low-cycle fatigue tests are conducted to verify the model. The prediction of the model agrees with the experimental results reasonably well.  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