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   39090篇
  免费   130篇
  国内免费   180篇
系统科学   248篇
丛书文集   445篇
教育与普及   104篇
理论与方法论   128篇
现状及发展   17123篇
研究方法   1650篇
综合类   19129篇
自然研究   573篇
  2013年   292篇
  2012年   611篇
  2011年   1178篇
  2010年   289篇
  2008年   719篇
  2007年   815篇
  2006年   798篇
  2005年   843篇
  2004年   798篇
  2003年   744篇
  2002年   704篇
  2001年   1260篇
  2000年   1235篇
  1999年   811篇
  1994年   377篇
  1992年   743篇
  1991年   605篇
  1990年   674篇
  1989年   614篇
  1988年   567篇
  1987年   631篇
  1986年   643篇
  1985年   805篇
  1984年   633篇
  1983年   556篇
  1982年   492篇
  1981年   493篇
  1980年   538篇
  1979年   1287篇
  1978年   996篇
  1977年   941篇
  1976年   736篇
  1975年   805篇
  1974年   1053篇
  1973年   911篇
  1972年   936篇
  1971年   1087篇
  1970年   1417篇
  1969年   1041篇
  1968年   974篇
  1967年   1006篇
  1966年   922篇
  1965年   653篇
  1959年   359篇
  1958年   582篇
  1957年   425篇
  1956年   380篇
  1955年   311篇
  1954年   323篇
  1948年   283篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In this paper, we introduce a new class of generalized convex function, namely, a-pseudounivex function, by combining the concepts of pseudo-univex and α-invex functions. Further, we establish some relationships between vector variational-like inequality problems and vector optimization problems under the assumptions of α-pseudo-univex functions. Results obtained in this paper present a refinement and improvement of previously known results.  相似文献   
82.
83.
84.
85.
After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems.  相似文献   
86.
Karyotypes of seven species of bats from Thailand (Chiroptera,Mammalia)   总被引:2,自引:0,他引:2  
Summary Karyotypes ofMyotis siligorensis, Myotis mystacinus, Pipistrellus pulveratus, Tylonycteris robustula, Miniopterus schreibersi fuliginosus, Hipposideros fulvus andAselliscus stoliczkanus from Thailand are investigated.Acknowledgment. The authors are very grateful to Dr N. Ratanawarabhan, Mrs S. Sittilert, P. Noonpakdee and S. Kuanchalern of Thailand Institute of Scientific and Technological Research for their valuable advice and assistance during our field survey in Thailand.  相似文献   
87.
On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5~7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2~10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the gri...  相似文献   
88.
With a unique corporate culture based on ancient Ch in ese wisdom being implemented at workplace for more than 10 years, we have been e ncountering various issue of managing conflicts, in particular at organization r estructure period, although we perceive that conflict does not necessarily have dysfunctional effect on our group performance. However, conflicts between and am ong various levels of the organization hierarchy are inevitably creating certain impact on our organization cohesiveness, performa...  相似文献   
89.
T R Garbe 《Experientia》1992,48(7):635-639
Invasive microorganisms encounter defensive attempts of the host to starve, destroy and eliminate the infection. In experimental model systems aiming to imitate defensive actions of the host, microorganisms respond by the rapid acceleration in the rate of expression of heat shock and other stress proteins. Heat shock proteins (hsp) of most if not all pathogens are major immune targets for both B- and T-cells. Host cells involved in the defensive action cannot avoid exposure to their own reactive compounds, such as oxygen radicals, resulting in premature cell death and tissue damage. Long-term consequences to the host may include cancer. In cells in tissue culture, induction of host-specific hsps occurs upon exposure to oxidants and in viral infections. Drugs that bind to members of the hsp70 family induce peroxisome proliferation and hepatocarcinoma, but may open the way for the development of novel drugs in support of antimetabolite treatment of infections and cancer.  相似文献   
90.
Acquired immunity and epidemiology of Schistosoma haematobium   总被引:1,自引:0,他引:1  
Human immune responses to schistosome infection have been characterized in detail. But there has been controversy over the relative importance of ecological factors (variation in exposure to infection) and immunological factors (acquired immunity) in determining the relationships between levels of infection and age typically found in areas where infection is endemic. Independent effects of exposure and age on the rates of reinfection with Schistosoma haematobium after chemotherapy have been demonstrated in the Gambia and Zimbabwe. This age effect could be the result of acquired immunity to infection. Indeed, allowing for variation in exposure and age, low rates of reinfection in the Gambia are correlated with high amounts of specific IgE antibodies--human IgE can kill S. mansoni schistosomulae in vitro. Further, animals can acquire immunologically mediated resistance to S. mansoni infection, although nonimmunological factors could also be involved. Acquisition of this immunity seems to be related to the cumulative effects of repeated infection and provides only partial protection. These characteristics are consistent with immuno-epidemiological data for both S. mansoni and S. haematobium infections of humans. We have now analysed age-prevalence data for human infection with S. haematobium, and find patterns of variation that are indeed consistent with the epidemiological effects of acquired immunity predicted by mathematical models.  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