全文获取类型
收费全文 | 112125篇 |
免费 | 29354篇 |
国内免费 | 26795篇 |
专业分类
化学 | 73660篇 |
晶体学 | 2205篇 |
力学 | 7486篇 |
综合类 | 1034篇 |
数学 | 14762篇 |
物理学 | 69127篇 |
出版年
2024年 | 561篇 |
2023年 | 1252篇 |
2022年 | 2132篇 |
2021年 | 2097篇 |
2020年 | 2295篇 |
2019年 | 2716篇 |
2018年 | 2627篇 |
2017年 | 3496篇 |
2016年 | 3548篇 |
2015年 | 4127篇 |
2014年 | 4346篇 |
2013年 | 6610篇 |
2012年 | 7319篇 |
2011年 | 8968篇 |
2010年 | 11983篇 |
2009年 | 12329篇 |
2008年 | 6412篇 |
2007年 | 5802篇 |
2006年 | 5326篇 |
2005年 | 5370篇 |
2004年 | 5570篇 |
2003年 | 4300篇 |
2002年 | 4196篇 |
2001年 | 4416篇 |
2000年 | 3686篇 |
1999年 | 3440篇 |
1998年 | 2713篇 |
1997年 | 2471篇 |
1996年 | 2742篇 |
1995年 | 3132篇 |
1994年 | 3164篇 |
1993年 | 3179篇 |
1992年 | 2722篇 |
1991年 | 2293篇 |
1990年 | 1968篇 |
1989年 | 2064篇 |
1988年 | 1979篇 |
1987年 | 1245篇 |
1986年 | 1295篇 |
1985年 | 940篇 |
1984年 | 1044篇 |
1982年 | 939篇 |
1981年 | 782篇 |
1980年 | 799篇 |
1979年 | 561篇 |
1978年 | 540篇 |
1977年 | 638篇 |
1976年 | 1044篇 |
1973年 | 440篇 |
1972年 | 533篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
文章详细描述了航空兵机场塔台辅助指挥系统之通信分系统设计的特点与功能、硬件结构、软件设计原则以及接口通信协议等问题。该分系统设计已在航空兵塔台辅助指挥系统研究中得到应用 ,并达到了良好的控制效果。 相似文献
182.
183.
184.
LI Cun YANG Bai-Feng CAI Hao HUANG Nian-Ning 《理论物理通讯》2006,46(2):244-248
One of the basic problems about the inverse scattering transform for solving a completely integrable nonlinear evolutions equation is to demonstrate that the Jost solutions obtained from the inverse scattering equations of Cauchy integral satisfy the Lax equations. Such a basic problem still exists in the procedure of deriving the dark soliton solutions of the NLS equation in normal dispersion with non-vanishing boundary conditions through the inverse scattering transform. In this paper, a pair of Jost solutions with same analytic properties are composed to be a 2 × 2 matrix and then another pair are introduced to be its right inverse confirmed by the Liouville theorem. As they are both 2 × 2 matrices, the right inverse should be the left inverse too, based upon which it is not difficult to show that these Jost solutions satisfy both the first and second Lax equations. As a result of compatibility condition, the dark soliton solutions definitely satisfy the NLS equation in normal dispersion with non-vanishing boundary conditions. 相似文献
185.
Utilization of carbohydrates by radiation processing 总被引:2,自引:0,他引:2
Upgrading and utilization of carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, pectin have been investigated for recycling these bio-resources and reducing the environmental pollution. These carbohydrates were easily degraded by irradiation and various kinds of biological activities such as anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction, etc. were induced. On the other hand, some carbohydrate derivatives, carboxymethylcellulose and carboxymethylstarch, could be crosslinked under certain radiation condition and produce the biodegradable hydrogel for medical and agricultural use. 相似文献
186.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
187.
Qiu Hong WU He Xiang WANG Kun GAO State Key Laboratory of Applied Organic Chemistry College of Chemistry Chemical Engineering Lanzhou University Lanzhou 《中国化学快报》2006,17(2)
Many Ligularia species have long been used as traditional folk medicine for theirantibiotic, antiphlogistic and antitussive activities1, and were found to be an importantsource of eremophilane. In the course of our search for bioactive sesquiterpenoids, w… 相似文献
188.
Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
189.
190.
Kj?rand Iversen Per Nilsson 《International Journal of Computers for Mathematical Learning》2007,12(2):113-133
This paper focuses on the different ways in which students in lower secondary school (14–16 year olds) experience compound
random events, presented to them in the form of combined junctions. A carefully designed ICT environment was developed enabling
the students to interact with different representations of such structures. Data for the analysis was gathered from two interview
sessions. The analysis of the interaction is based on constructivist principles on learning; i.e. we adopted a student-oriented
perspective, taking into consideration the different ways students try to make sense of chance encounters.
Our results show how some students give priority to geometrical and physical concerns, and we discuss how seeking causal explanations
of random phenomena may have encouraged this. With respect to numerically oriented models a division strategy appears to stand
out as the preferred one. 相似文献