全文获取类型
收费全文 | 36697篇 |
免费 | 641篇 |
国内免费 | 70篇 |
专业分类
系统科学 | 1203篇 |
丛书文集 | 717篇 |
教育与普及 | 79篇 |
理论与方法论 | 457篇 |
现状及发展 | 14283篇 |
研究方法 | 1358篇 |
综合类 | 18941篇 |
自然研究 | 370篇 |
出版年
2018年 | 765篇 |
2017年 | 771篇 |
2016年 | 505篇 |
2012年 | 675篇 |
2011年 | 1757篇 |
2010年 | 984篇 |
2009年 | 581篇 |
2008年 | 1053篇 |
2007年 | 1287篇 |
2006年 | 605篇 |
2005年 | 634篇 |
2004年 | 643篇 |
2003年 | 723篇 |
2002年 | 623篇 |
2001年 | 979篇 |
2000年 | 902篇 |
1999年 | 599篇 |
1992年 | 569篇 |
1991年 | 465篇 |
1990年 | 486篇 |
1989年 | 489篇 |
1988年 | 490篇 |
1987年 | 498篇 |
1986年 | 490篇 |
1985年 | 599篇 |
1984年 | 495篇 |
1983年 | 406篇 |
1982年 | 346篇 |
1981年 | 342篇 |
1980年 | 448篇 |
1979年 | 968篇 |
1978年 | 855篇 |
1977年 | 846篇 |
1976年 | 582篇 |
1975年 | 631篇 |
1974年 | 932篇 |
1973年 | 786篇 |
1972年 | 804篇 |
1971年 | 1017篇 |
1970年 | 1339篇 |
1969年 | 1004篇 |
1968年 | 945篇 |
1967年 | 990篇 |
1966年 | 829篇 |
1965年 | 610篇 |
1959年 | 360篇 |
1958年 | 522篇 |
1957年 | 443篇 |
1956年 | 366篇 |
1954年 | 363篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
36.
Rein Vihalemm 《Foundations of Science》2007,12(3):223-234
The philosophical analysis of chemistry has advanced at such a pace during the last dozen years that the existence of philosophy of chemistry as an autonomous discipline cannot be doubted any more. The present paper will attempt to analyse the experience of philosophy of chemistry at the, so to say, meta-level. Philosophers of chemistry have especially stressed that all sciences need not be similar to physics. They have tried to argue for chemistry as its own type of science and for a pluralistic understanding of science in general. However, when stressing the specific character of chemistry, philosophers do not always analyse the question ‘What is science?’ theoretically. It is obvious that a ‘monistic’ understanding of science should not be based simply on physics as the epitome of science, regarding it as a historical accident that physics has obtained this status. The author’s point is that the philosophical and methodological image of science should not be chosen arbitrarily; instead, it should be theoretically elaborated as an idealization (theoretical model) substantiated on the historical practice of science. It is argued that although physics has, in a sense, justifiably obtained the status of a paradigm of science, chemistry, which is not simply a physical science, but a discipline with a dual character, is also relevant for elaborating a theoretical model of science. The theoretical model of science is a good tool for examining various issues in philosophy of chemistry as well as in philosophy of science or science studies generally. 相似文献
37.
Global Optimization in Any Minkowski Metric: A Permutation-Translation Simulated Annealing Algorithm for Multidimensional Scaling 总被引:3,自引:1,他引:2
It is well known that considering a non-Euclidean Minkowski metric in Multidimensional Scaling, either for the distance model
or for the loss function, increases the computational problem of local minima considerably. In this paper, we propose an algorithm
in which both the loss function and the composition rule can be considered in any Minkowski metric, using a multivariate randomly
alternating Simulated Annealing procedure with permutation and translation phases. The algorithm has been implemented in Fortran
and tested over classical and simulated data matrices with sizes up to 200 objects. A study has been carried out with some
of the common loss functions to determine the most suitable values for the main parameters. The experimental results confirm
the theoretical expectation that Simulated Annealing is a suitable strategy to deal by itself with the optimization problems
in Multidimensional Scaling, in particular for City-Block, Euclidean and Infinity metrics. 相似文献
38.
39.
40.
Enzymatic control of cell division in micro-organisms 总被引:1,自引:0,他引:1
NICKERSON WJ 《Nature》1948,162(4111):241-245