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   44072篇
  免费   147篇
  国内免费   289篇
系统科学   538篇
丛书文集   1032篇
教育与普及   143篇
理论与方法论   243篇
现状及发展   17817篇
研究方法   1649篇
综合类   22247篇
自然研究   839篇
  2013年   443篇
  2012年   794篇
  2011年   1657篇
  2010年   504篇
  2009年   454篇
  2008年   955篇
  2007年   1035篇
  2006年   1079篇
  2005年   1026篇
  2004年   814篇
  2003年   766篇
  2002年   780篇
  2001年   1244篇
  2000年   1212篇
  1999年   825篇
  1992年   734篇
  1991年   610篇
  1990年   629篇
  1989年   612篇
  1988年   615篇
  1987年   615篇
  1986年   592篇
  1985年   726篇
  1984年   624篇
  1983年   504篇
  1982年   456篇
  1981年   444篇
  1980年   569篇
  1979年   1237篇
  1978年   1059篇
  1977年   1070篇
  1976年   759篇
  1975年   857篇
  1974年   1223篇
  1973年   1062篇
  1972年   1062篇
  1971年   1311篇
  1970年   1646篇
  1969年   1291篇
  1968年   1232篇
  1967年   1301篇
  1966年   1116篇
  1965年   822篇
  1959年   487篇
  1958年   708篇
  1957年   567篇
  1956年   475篇
  1955年   440篇
  1954年   468篇
  1948年   246篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
The developmental dynamics of the maize leaf transcriptome   总被引:5,自引:0,他引:5  
  相似文献   
912.
Psoriatic arthritis (PsA) is an inflammatory joint disease that is distinct from other chronic arthritides and which is frequently accompanied by psoriasis vulgaris (PsV) and seronegativity for rheumatoid factor. We conducted a genome-wide association study in 609 German individuals with PsA (cases) and 990 controls with replication in 6 European cohorts including a total of 5,488 individuals. We replicated PsA associations at HLA-C and IL12B and identified a new association at TRAF3IP2 (rs13190932, P = 8.56 × 10?1?). TRAF3IP2 was also associated with PsV in a German cohort including 2,040 individuals (rs13190932, P = 1.95 × 10?3). Sequencing of the exons of TRAF3IP2 identified a coding variant (p.Asp10Asn, rs33980500) as the most significantly associated SNP (P = 1.13 × 10?2?, odds ratio = 1.95). Functional assays showed reduced binding of this TRAF3IP2 variant to TRAF6, suggesting altered modulation of immunoregulatory signals through altered TRAF interactions as a new and shared pathway for PsA and PsV.  相似文献   
913.
914.
915.
Les observatoires occidentaux se transforment en véritable usine scientifique à partir du milieu du 19e siècle. L'astrométrie symbolise ce passage à une économie industrieuse des pratiques scientifiques. Le chronographe imprimant, qui permet de réduire les équations personnelles des observateurs, s'impose, d'abord aux Etats-Unis, puis en Angleterre, en instrument-emblème de cette transformation profonde. En France, les initiatives de l'astronome Liais restent prototypiques. Ce n'est qu'au début du 20e siècle, par les voies détournées de l'observatoire d'Hendaye et de l'abbé Verschaffel, que le chronographe imprimant fait son retour et conquiert les espaces savants. La centralisation excessive de l'astronomie française, l'autoritarisme du directeur de l'Observatoire de Paris Urbain Le Verrier, et la faiblesse du marché des instruments expliquent pourquoi le chronographe imprimant n'a fait souche que très tardivement en France.  相似文献   
916.
917.
918.
In the history of chemistry, the Danish chemist Julius Thomsen (1826–1909) is best known for his contributions to thermochemistry. Throughout his life, he was a pronounced atomist and a tireless advocate of neo-Proutian views as to the constitution of matter. On many occasions, especially in his later years, he engaged in speculations concerning the unity of matter and the complexity of atoms. In this engagement, Thomsen was alone in Danish chemistry, but his works were representative of a large number of 19th-century chemists, particularly in England and Germany. Thomsen's ideas as to the constitution of matter, the periodic system and the noble gases, may be seen as typical of this vigorous trend in fin de siècle chemistry.  相似文献   
919.
We present an analysis, and first full English translation, of a paper by Kant entitled ‘Über die Vulcane im Monde’ (1785). Kant became interested in the question of whether the mountains of the Moon were extinct volcanoes. Stimulated by the work of Herschel, Aepinus, and others, he considered the appearance of the Moon's surface and the possibility of lunar vulcanism. From this, he was led to consider the structures of mountain ranges on the Earth, which he decided were non-volcanic in origin, being produced by eruptions of vapours from the interior of the Earth soon after it formed from an original ‘chaos’. Kant developed his ideas in such a way as to yield a characteristic eighteenth-century ‘theory of the Earth’. We argue that the empirical base of his theory was provided by knowledge of the mountain ranges of Bohemia and Moravia. Analogies based on observations of the Moon further assisted in the construction of the theory. But the reasoning ran in two directions: what was seen on the Moon was construed in terms of what Kant knew of the Earth's topography; and the Earth's topography was presumed to be analogous to that of the Moon, for both the Earth and the Moon (and indeed all heavenly bodies) supposedly had essentially similar origins. Kant's ideas of 1785 are related to his earlier writings of 1754, 1755, and 1756, and also to the lectures on physical geography that he presented at Königsberg.  相似文献   
920.
This article attempts a contextual study of the origin and early development of August Kekulé's theory of aromatic compounds. The terminus a quo is essentially August Hofmann's coining of the modern chemical denotation of ‘aromatic’ in 1855; the terminus ad quem is the first full codification of Kekulé's theory in the sixth fascicle of his Lehrbuch der organischen Chemie, published in the summer of 1866. Kekulé's theory is viewed in context with the earlier and concurrent experimental work of such chemists as Hermann Kolbe, Friedrich Beilstein, Rudolph Fittig, and Hugo Müller. The reception of the theory is briefly examined. Attention is paid to the role of Kekulé's molecular models and of his celebrated dream anecdote of the snake that seizes its own tail. The episode is used as a case study for the continuity of scientific progress, and to illustrate the close reciprocal interactions of hypothesis and experiment in the evolution of a scientific theory.  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