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   446395篇
  免费   6323篇
  国内免费   1849篇
电工技术   7812篇
综合类   714篇
化学工业   67761篇
金属工艺   18182篇
机械仪表   14050篇
建筑科学   10918篇
矿业工程   2838篇
能源动力   11536篇
轻工业   39648篇
水利工程   4956篇
石油天然气   9765篇
武器工业   61篇
无线电   52937篇
一般工业技术   88198篇
冶金工业   78488篇
原子能技术   9659篇
自动化技术   37044篇
  2021年   4107篇
  2020年   3025篇
  2019年   3727篇
  2018年   6280篇
  2017年   6337篇
  2016年   6913篇
  2015年   4459篇
  2014年   7465篇
  2013年   20274篇
  2012年   12267篇
  2011年   16581篇
  2010年   13175篇
  2009年   14608篇
  2008年   15201篇
  2007年   15009篇
  2006年   13517篇
  2005年   12223篇
  2004年   11492篇
  2003年   11274篇
  2002年   10680篇
  2001年   11067篇
  2000年   10118篇
  1999年   10634篇
  1998年   25418篇
  1997年   17812篇
  1996年   13587篇
  1995年   10345篇
  1994年   8996篇
  1993年   9090篇
  1992年   6711篇
  1991年   6436篇
  1990年   6193篇
  1989年   6019篇
  1988年   5911篇
  1987年   4932篇
  1986年   4907篇
  1985年   5792篇
  1984年   5292篇
  1983年   4923篇
  1982年   4495篇
  1981年   4517篇
  1980年   4391篇
  1979年   4282篇
  1978年   4134篇
  1977年   4534篇
  1976年   5501篇
  1975年   3689篇
  1974年   3460篇
  1973年   3626篇
  1972年   3000篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
This paper considers processes of organizational imprintingin a sample of 100 young, high technology companies. It examinesthe effects of a pair of initial conditions: the founders' modelsof the employment relation and their business strategies. Ouranalyses indicate that these two features were well alignedwhen the firms were founded. However, the alignment has deterioratedover time, due to changes in the distribution of employmentmodels. In particular, the ‘star’ model and ‘commitment’model are less stable than the ‘engineering’ modeland the ‘factory’ model. Despite their instability,these two blueprints for the employment relation have strongeffects in shaping the early evolution of these firms. In particular,firms that embark with these models have significantly higherrates of replacing the founder chief executive with a non-founderas well as higher rates of completing an initial public stockoffering. Some implications of these findings for future studiesof imprinting and inertia in organizations are discussed.  相似文献   
992.
We cloned the Saccharomyces kluyveri HIS3 homolog, k-HIS3, and made a partial deletion of the gene. The k-HIS3 gene complemented a HIS3 deletion in S. cerevisiae. The DNA sequences of the open reading frames (ORFs) of the HIS3 homologs are 70% identical at the DNA level and 83% identical at the deduced amino acid level. The ORF upstream of the k-HIS3 gene is related to the PET56 gene of S. cerevisiae found upstream of the HIS3 gene of S. cerevisiae. The ORF downstream from the k-HIS3 gene is not related to the DED1 gene found downstream of the HIS3 gene in S. cerevisiae.  相似文献   
993.
Magnetic characterization has been performed on the members of the cuprateniobate RBa2Cu2NbO8 (R = Pr, Nd, and La) series and R1.5Ce0.5Sr2Cu2NbO10 (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K. The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting NdCSCNO, SmCSCNO, and EuCSCNO compounds.  相似文献   
994.
Polyarteritis nodosa is a rare disorder and a form of systemic vasculitis. A 48 year-old female was admitted to the hospital because menorrhagia and pelvic pain in February 1993. The patient underwent exploratory laparotomy resulting in a total hysterectomy and bilateral salpingo-oophorectomy for myoma of uterus and a right adnexal cystic mass. Histopathologic examination revealed left ovarian periarteritis nodosa. Further investigation and 9 months follow-up failed to show any systemic involvement. To our knowledge the isolated ovarian polyarteritis nodosa is the first case in the literature.  相似文献   
995.
Methods are described for forming coating specimens and testing them in pure bending. The proposed tester gives adequate accuracy in determining the elastic characteristics and strength for thin specimens (up to 0.1 mm) of brittle materials of powder-coating type.Translated from Problemy Prochnosti, No. 3, pp. 94–97, March, 1993.  相似文献   
996.
997.
For psychological reasons, coelocentesis was performed in 20 women prior to termination of pregnancy, at 6-11 weeks of gestation. The fetal heart rate (FHR) was measured immediately before the procedure and at 1, 5, and 10 min afterward. There was no significant difference between FHR before coelocentesis compared to the values at 1 min (mean = 158, range 114-178; z = -0.629, P = 0.529), 5 min (mean = 160, range 121-179; z = -0.191, P = 0.848), or 10 min (mean 159, range 117-183; z = -0.214, P = 0.83) after the procedure. These findings suggest that coelocentesis does not have a major effect on the fetal cardiovascular system.  相似文献   
998.
999.
1000.
MCF7 and ZR75-1 breast cancer cells grow as adherent monolayers in tissue culture. Treatment with the serum serine protease plasmin causes them to detach and to grow as floating multicellular spheroids. Two plasmin activators, urokinase plasminogen activator and streptokinase, induce the same growth pattern changes in the presence of plasminogen. Serum contains also plasminogen activator inhibitors. Aged serum, deficient in plasminogen activator inhibitors, converts spontaneously monolayer breast cancer cells into multicellular spheroids which readily revert to monolayer growth after addition of fresh serum. Urokinase blocks the reversion. The formation of multicellular spheroids does not affect the proliferative rate of breast tumor cells but endows tumor cells with increased resistance to the chemotherapeutic drugs, doxorubicin and paclitaxel.  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