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   1411篇
  免费   4篇
  国内免费   14篇
系统科学   108篇
丛书文集   2篇
教育与普及   10篇
理论与方法论   27篇
现状及发展   228篇
研究方法   191篇
综合类   751篇
自然研究   112篇
  2020年   5篇
  2019年   6篇
  2018年   8篇
  2017年   12篇
  2016年   7篇
  2015年   10篇
  2014年   10篇
  2013年   34篇
  2012年   106篇
  2011年   224篇
  2010年   37篇
  2009年   7篇
  2008年   95篇
  2007年   96篇
  2006年   85篇
  2005年   120篇
  2004年   109篇
  2003年   100篇
  2002年   93篇
  2001年   16篇
  2000年   14篇
  1999年   19篇
  1998年   13篇
  1997年   6篇
  1996年   7篇
  1995年   14篇
  1993年   5篇
  1992年   19篇
  1991年   7篇
  1990年   8篇
  1989年   6篇
  1988年   7篇
  1986年   6篇
  1985年   10篇
  1984年   4篇
  1983年   5篇
  1982年   9篇
  1979年   7篇
  1978年   4篇
  1977年   4篇
  1974年   5篇
  1970年   4篇
  1967年   4篇
  1966年   4篇
  1965年   3篇
  1958年   4篇
  1957年   4篇
  1956年   4篇
  1954年   4篇
  1948年   4篇
排序方式: 共有1429条查询结果,搜索用时 265 毫秒
931.
围绕审知法采的连系性,考夫曼将演绎、归纳、骈推与比类连成体系。其中,演绎为仆,比类是首脑,归纳辅佐,骈推守护清白。演绎在审判训疏与说服总系统中是协和元。考夫曼归纳观的归宿是对旧的律意说服的重新组织。其创新点是说服的三阶式。他的贡献是以逻辑组织连系骈推与演绎。考夫曼认为,法采进程的本质不是逻辑推合,而是比较。律令的颁布与司法中逻辑组织的相似性在于其比类基础。考察了考夫曼比较点的选择后显示,不可抹煞两领域之间的红线。认为考夫曼的重大贡献是将比类引入审判陈说的总组织,它是原省、衡议后的第三元。在论述的基础上,为比类设定了两则对行的准法。  相似文献   
932.
Editorial     
Systemic Practice and Action Research -  相似文献   
933.
Generalized Partial Computation (GPC) is a program transformation method utilizing partial information about input data, properties of auxiliary functions and the logical structure of a source program. GPC uses both an inference engine such as a theorem prover and a classical partial evaluator to optimize programs. Therefore, GPC is more powerful than classical partial evaluators but harder to implement and control. We have implemented an experimental GPC system called WSDFU (Waseda Simplify-Distribute-Fold-Unfold). This paper discusses the power of the program transformation system, its theorem prover and future works.  相似文献   
934.
935.
936.
Climbing behavior is poorly documented in skunk species, with the exception of the genus Spilogale. Herein we describe 2 cases of climbing behavior in the American hog-nosed skunk ( Conepatus leuconotus ): one in Colima, Mexico, and another in west central Texas, USA. In both cases, a male climbed over 5 m into oak trees when pursued by humans. Climbing as an escape behavior in hog-nosed skunks has not previously been reported.  相似文献   
937.
The little-known mayfly Siphlonurus autumnalis McDunnough (Ephemeroptera: Siphlonuridae) was collected from several locations in its floodplain habitats along the Middle Fork of the Flathead River in western Montana. To confirm identification, nymphs were reared along with an associated species, S. occidentalis Eaton (Ephemeroptera: Siphlonuridae). Adults emerged from 6 September until 16 October. Habitats are described and the first photos of the 2 sexes are provided.  相似文献   
938.
A list of one taxon new for Montana and 10 new for Wyoming is presented, plus comments about Astragalus molybdenus.  相似文献   
939.
We compared winter (December, January, and February) and early spring (March and April) bird communities among 4 successional stages that included grassland, shrubsteppe, juniper-shrubsteppe, and old-growth juniper woodland in central Oregon. Birds were surveyed monthly from December through April in 1998/1999 and 1999/2000 using the point count method to estimate relative abundance of birds (individuals ? transect –1 year –1 ). We used distance sampling to correct for potential bias in estimating abundance and density among successional stages. A total of 4513 birds (32 species) were detected. Relative abundance of total birds (all species combined) was similar in the juniper-shrubsteppe and old-growth woodland (48.7 and 48.9 individuals ? transect –1 , respectively) but 6 times greater than in the grassland and shrubsteppe (8.0 and 7.7 individuals ? transect –1 , respectively) during the 5-month period. Total density of birds was greater in old-growth juniper woodland and juniper-shrubsteppe than in grassland or shrubsteppe. However, median bird species richness in 1998/1999 was highest in grassland and lowest both in shrubsteppe and juniper-shrubsteppe, and in 1999/2000 it was highest in shrubsteppe and lowest in juniper-shrubsteppe and oldgrowth juniper woodland. American Robins and Townsend's Solitaires were the most abundant species in junipershrubsteppe and old-growth juniper woodland during the winter months. Sage Sparrows and Horned Larks were the most abundant species in shrubsteppe during winter, and Horned Larks were most abundant in grasslands during the early spring transition period prior to nesting. Our results indicate that a different suite of species use these successional stages during the nonbreeding season. If avifauna conservation is a part of long-term management goals, a broad range of successional stages should be maintained on the landscape to provide habitat for a variety of avian species throughout the year.  相似文献   
940.
Numerous basins of the intermountain area often have extensive playa surfaces that are nearly devoid of vegetation. Margins of these playas support sparse communities dominated by chenopod shrubs Allenrolfea occidentalis (iodine bush) and Sacrobatus vermiculatus (black greasewood). These plants establish and persist in an environment where halomorphic soils induce extreme osmotic stress and atmospheric precipitation is very low and erratic and occurs largely during the winter when temperatures are too low for growth. We measured net CO 2 assimilation rates, leaf conductances, transpiration rates, water-use efficiencies, and stem xylem potentials for these two C3 species. Data were collected in above-average (1991) and below-average (1992) precipitation years. Net CO 2 assimilation rates for Allenrolfea were statistically similar in 1991 and 1992 but in general declined for Sarcobatus in 1992. For both species, leaf conductances and leaf transpiration rates declined significantly from 1991 to 1992, with the decline greater for Sarcobatus . Water-use efficiencies doubled from 1991 to 1992 for both plant species. Predawn xylem water potentials were -2.2 and -3.3 MPa for Allenrolfea and -1.8 and -2.6 MPa for Sarcobatus by September 1991 and 1992, respectively. Afternoon xlem water potentials were -3.1 and -2.0 MPa for Allrolfea and -2.6 and -2.2 for Sarcobatus beginning in May 1991 and 1992, respectively. Xylem water potentials dropped to -5.0 MPa for Allenrolfea and -3.4 MPa for Sarcobatus by September for both 1991 and 1992. For Allenrolfea , in general, the total soil water potential within the zone of maximum root activity is more negative than the plant's predawn xylem potential, which suggests that the plant is partially phreatophytic and/or has a large capacitance due to its extensive woody root system.  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