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   1155692篇
  免费   118433篇
  国内免费   1658篇
  2018年   19511篇
  2017年   17894篇
  2016年   19111篇
  2015年   18274篇
  2014年   21017篇
  2013年   29934篇
  2012年   36699篇
  2011年   44479篇
  2010年   32900篇
  2009年   27896篇
  2008年   37945篇
  2007年   40179篇
  2006年   29148篇
  2005年   28427篇
  2004年   28649篇
  2003年   27585篇
  2002年   26601篇
  2001年   48298篇
  2000年   48804篇
  1999年   38908篇
  1998年   13864篇
  1997年   14474篇
  1996年   13483篇
  1995年   12733篇
  1994年   12380篇
  1993年   12302篇
  1992年   31990篇
  1991年   31117篇
  1990年   30348篇
  1989年   29587篇
  1988年   27804篇
  1987年   26042篇
  1986年   24337篇
  1985年   24357篇
  1984年   20270篇
  1983年   17197篇
  1982年   13334篇
  1981年   12100篇
  1980年   11204篇
  1979年   18954篇
  1978年   15012篇
  1977年   13632篇
  1976年   12566篇
  1975年   14039篇
  1974年   15253篇
  1973年   15099篇
  1972年   13857篇
  1971年   12744篇
  1970年   10727篇
  1969年   10513篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
941.
Experimental projects have demonstrated the technical feasibility of systems of accessible, affordable health care. These projects have relied extensively on non-professional community health workers. However, large-scale implementation of these schemes will require new management procedures that are both responsive to rural health needs and congruent with national institutions. This paper identifies the need to establish institutional mechanisms to mobilize essential inputs, promote acceptance by beneficiaries, maintain quality standards, recruit and retain field staff, and achieve accountability for resources. It then outlines methods for developing these institutions. It stresses the need for both formal, bureaucratic organizations and informal organizations of clients. It also identifies the need to consider administrative and institutional resources in determining the appropriateness of a health care technology.  相似文献   
942.
943.
A spectroscopic method employing pulsed dye laser instrumentation is described for the determination of the 1H2O/2H2O composition of aqueous solutions by the measurement of reciprocal excited state lifetimes of EuEDTA-. The reciprocal lifetimes, gamma-1, of the 1H2O/2H2O mixtures increase linearly with the mole fraction of 1H2O. For EuEDTA- the relationship between gamma-1 and the mole fraction, chi H, of 1H2O in 1H2O/2H2O mixtures is expressed by the equation chi H = 0.37 gamma-1-0.152, with a sensitivity in chi H of +/- 0.02. The reciprocal lifetimes are independent of pH in the range 5.1 to 10.5, changes in ionic strength, and the type of buffer used in EuEDTA- containing solutions.  相似文献   
944.
945.
946.
947.
948.
949.
950.
The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately these data have until now been scattered throughout the literature in a variety of books, proceedings and journals. The data have recently been compiled in a centralized database, LIPIDAT, with a view to providing ready access to the data and to the appropriate literature. LIPIDAT consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically-derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc., on the thermodynamic values. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes comprehensive literature referencing and list of authors, but does not at the present time include article titles. As of this writing, the database is current through June, 1990 and is approaching 10,000 records in length. Each record contains 28 fields. In this paper we report the contents and present an analysis of LIPIDAT as it refers to fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). This database subset represents about 7% of all LIPIDAT records. It includes data collected over a 23-year period from 1967 to 1989 and consists of 702 records obtained from 336 articles in 55 different journals. The number of records per year rises steadily beginning in 1971, reaches a maximum of 89 records/year in 1977 and remains relatively constant at 60-70 records/year in the succeeding period. Journals making the greatest contribution to the DMPC subset include Biochimica et Biophysica Acta, Biochemistry, Chemistry and Physics of Lipids and the Biophysical Journal. These four journals account for 71% of the total records in the database subset. The analysis shows that differential scanning calorimetry, electron spin resonance, fluorescence, nuclear magnetic resonance and Raman spectroscopy are the methods most commonly used for DMPC transition temperature determination. An interesting pattern emerges as to the place in time the different methods assume or loose popularity.(ABSTRACT TRUNCATED AT 400 WORDS)  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