全文获取类型
收费全文 | 283012篇 |
免费 | 28484篇 |
国内免费 | 28037篇 |
专业分类
化学 | 120290篇 |
晶体学 | 4194篇 |
力学 | 22848篇 |
综合类 | 3799篇 |
数学 | 83172篇 |
物理学 | 105230篇 |
出版年
2023年 | 2619篇 |
2022年 | 5918篇 |
2021年 | 6007篇 |
2020年 | 6287篇 |
2019年 | 6338篇 |
2018年 | 5790篇 |
2017年 | 6927篇 |
2016年 | 7579篇 |
2015年 | 6456篇 |
2014年 | 10268篇 |
2013年 | 17532篇 |
2012年 | 11997篇 |
2011年 | 13938篇 |
2010年 | 12639篇 |
2009年 | 19444篇 |
2008年 | 20751篇 |
2007年 | 19531篇 |
2006年 | 17586篇 |
2005年 | 14279篇 |
2004年 | 13222篇 |
2003年 | 12363篇 |
2002年 | 14249篇 |
2001年 | 9867篇 |
2000年 | 9243篇 |
1999年 | 8259篇 |
1998年 | 7230篇 |
1997年 | 5963篇 |
1996年 | 5252篇 |
1995年 | 5230篇 |
1994年 | 4820篇 |
1993年 | 3960篇 |
1992年 | 3403篇 |
1991年 | 2641篇 |
1990年 | 2107篇 |
1989年 | 1813篇 |
1988年 | 1732篇 |
1987年 | 1253篇 |
1986年 | 949篇 |
1985年 | 1833篇 |
1984年 | 1380篇 |
1983年 | 894篇 |
1982年 | 1310篇 |
1981年 | 1414篇 |
1980年 | 1206篇 |
1979年 | 1108篇 |
1978年 | 949篇 |
1977年 | 814篇 |
1976年 | 755篇 |
1974年 | 493篇 |
1973年 | 643篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
2.
《Mendeleev Communications》2022,32(1):126-128
3-Aryl-5-methylidene-2-thiohydantoins were constructed in one-pot reaction of aryl isothiocyanates and 3-morpholino- alanine in alkaline medium with the subsequent treatment with boiling hydrochloric acid. 相似文献
3.
Dan Chen Kaixin Du Xiaochen Niu Hongwei Zhang Xue Zhang Yu Tang Jianchun Zhao 《Biomedical chromatography : BMC》2022,36(3):e5288
Amlexanox, an anti-inflammatory and anti-allergic agent, has been widely used clinically for the treatment of canker sores, asthma, and allergic rhinitis. Recently, amlexanox has received considerable attention in curing nonalcoholic fatty liver diseases and hepatitis virus infection. Herein, we first established a sensitive high-performance liquid chromatography-tandem mass spectrum (LC–MS/MS) method for the determination of amlexanox in rat plasma. Propranolol was used as the internal standard (IS). Using a simple protein precipitation method, the amlexanox and IS were separated with Capcell Pak C18 column (2.0 × 50 mm, 5 μm) and eluted with water and acetonitrile each containing 0.1% formic acid using gradient elution condition at a flow rate of 0.4 mL·min−1. Amlexanox and IS were detected by a triple quadrupole mass in multiple reactive monitoring (MRM) under the transitions of m/z 299.2 → 281.2 and m/z 259.9 → 116.1 with positive electrospray ionization, respectively. The calibration curves of amlexanox were established with the range of 50 to 2000 ng·mL−1 (r2 > 0.99). The validation method consisted of selectivity, accuracy, precision, carryover effect, matrix effect, recovery, dilution effect, and stability. The fully validated method was successfully applied to the pharmacokinetic study of amlexanox in Wistar rats. 相似文献
4.
This paper is concerned with the Cauchy problem on the Boltzmann equation without angular cutoff assumption for hard potential in the whole space. When the initial data is a small perturbation of a global Maxwellian, the global existence of solution to this problem is proved in unweighted Sobolev spaces with . But if we want to obtain the optimal temporal decay estimates, we need to add the velocity weight function, in this case the global existence and the optimal temporal decay estimate of the Boltzmann equation are all established. Meanwhile, we further gain a more accurate energy estimate, which can guarantee the validity of the assumption in Chen et al. (0000). 相似文献
5.
6.
《Operations Research Letters》2022,50(2):137-144
In mine planning problems, cutoff grade optimization defines a threshold at every time period such that material above this value is processed, and the rest is considered waste. In orebodies with multiple minerals, which occur in practice, the natural extension is to consider a cutoff surface. We show that in two dimensions the optimal solution is a line, and in n dimensions it is a hyperplane. 相似文献
7.
为提高煤与瓦斯突出矿井瓦斯抽放效果,建立了3个一级指标、14个二级指标的突出矿井瓦斯抽放限制影响因素评价指标体系,利用AHP和熵权法分别确定指标因子主、客观权重.通过实地调研分析和反馈验证了AHP-熵权法的可行性和正确性,利用加权平均法确定评价模型的综合权重.研究表明:封孔方式、钻孔半径、抽放时间、煤体裂隙发育程度和抽放负压是目前影响煤矿瓦斯抽放效果的主控因素. 相似文献
8.
Prof. Dr. Peter Hess 《Chemphyschem》2022,23(6):e202100880
In the periodic table the position of each atom follows the ‘aufbau’ principle of the individual electron shells. The resulting intrinsic periodicity of atomic properties determines the overall behavior of atoms in two-dimensional (2D) bonding and structure formation. Insight into the type and strength of bonding is the key in the discovery of innovative 2D materials. The primary features of 2D bonding and the ensuing monolayer structures of the main-group II–VI elements result from the number of valence electrons and the change of atom size, which determine the type of hybridization. The results reveal the tight connection between strength of bonding and bond length in 2D networks. The predictive power of the periodic table reveals general rules of bonding, the bonding-structure relationship, and allows an assessment of published data of 2D materials. 相似文献
9.
10.
This paper infers from a generalized Picone identity the uniqueness of the stable positive solution for a class of semilinear equations of superlinear indefinite type, as well as the uniqueness and global attractivity of the coexistence state in two generalized diffusive prototypes of the symbiotic and competing species models of Lotka–Volterra. The optimality of these uniqueness theorems reveals the tremendous strength of the Picone identity. 相似文献