全文获取类型
收费全文 | 446395篇 |
免费 | 6323篇 |
国内免费 | 1849篇 |
专业分类
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 |
出版年
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.
Inertia and Change in the Early Years: Employment Relations in Young, High Technology Firms 总被引:2,自引:0,他引:2
HANNAN MICHAEL T.; BURTON M. DIANE; BARON JAMES N. 《Industrial and Corporate Change》1996,5(2):503-536
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 commitmentmodel 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.
M. Bennahmias H. B. Radousky T. J. Goodwin R. N. Shelton 《Journal of Electronic Materials》1993,22(10):1189-1193
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.
G Makrydimas D Lolis I Georgiou C Skendou KH Nicolaides 《Canadian Metallurgical Quarterly》1997,6(6):314-316
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.
C Kooli M Salem A Hamzaoui M Fredj Z Kaouache N Khalfallah A Chabbou A Haddad 《Canadian Metallurgical Quarterly》1997,53(1):51-56
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