全文获取类型
收费全文 | 42484篇 |
免费 | 2777篇 |
国内免费 | 3086篇 |
专业分类
化学 | 34293篇 |
晶体学 | 465篇 |
力学 | 2201篇 |
综合类 | 234篇 |
数学 | 4601篇 |
物理学 | 6553篇 |
出版年
2024年 | 63篇 |
2023年 | 995篇 |
2022年 | 935篇 |
2021年 | 1126篇 |
2020年 | 2530篇 |
2019年 | 2086篇 |
2018年 | 1958篇 |
2017年 | 2040篇 |
2016年 | 2400篇 |
2015年 | 1907篇 |
2014年 | 2144篇 |
2013年 | 6058篇 |
2012年 | 2493篇 |
2011年 | 1832篇 |
2010年 | 1604篇 |
2009年 | 1870篇 |
2008年 | 1661篇 |
2007年 | 1854篇 |
2006年 | 1571篇 |
2005年 | 1393篇 |
2004年 | 1265篇 |
2003年 | 1057篇 |
2002年 | 863篇 |
2001年 | 718篇 |
2000年 | 666篇 |
1999年 | 568篇 |
1998年 | 534篇 |
1997年 | 486篇 |
1996年 | 412篇 |
1995年 | 503篇 |
1994年 | 376篇 |
1993年 | 349篇 |
1992年 | 289篇 |
1991年 | 219篇 |
1990年 | 202篇 |
1989年 | 173篇 |
1988年 | 197篇 |
1987年 | 206篇 |
1986年 | 128篇 |
1985年 | 114篇 |
1984年 | 121篇 |
1983年 | 35篇 |
1982年 | 79篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 45篇 |
1978年 | 30篇 |
1977年 | 23篇 |
1976年 | 18篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
1.
《Expositiones Mathematicae》2022,40(2):357-394
We give an informal exposition of pushforwards and orientations in generalized cohomology theories in the language of spectra. The whole note can be seen as an attempt at convincing the reader that Todd classes in Grothendieck–Hirzebruch–Riemann–Roch type formulas are not Devil’s appearances but rather that things just go in the most natural possible way. 相似文献
2.
3.
Zhi Sun Mengfan Zhao Lihua Zuo Shengnan Zhou Feng Fan Qingquan Jia Lianping Xue Hanbing Li Jian Kang Xiaojian Zhang 《Journal of separation science》2022,45(2):518-528
Juglandis Mandshuricae Cortex is the bark of Juglans mandshurica Maxim., which has been used as a folk medicine plant in China and India. In this study, an ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry method was developed to clarify and quantify the chemical profiling of Juglandis Mandshuricae Cortex rapidly. A total of 113 compounds were characterized. Among them, seven flavonoids were simultaneously quantified in 15 min, including myricetin, myricetrin, taxifolin, kaempferol, quercetin, quercitrin, and naringenin. The method was validated for accuracy, precision, and the limits of detection and quantification. All calibration curves showed a good linear relationship (r > 0.9990) within test ranges. The intra- and inter-day relative standard deviations were less than 2.16%. Accuracy validation showed that the recovery was between 95.6 and 101.3% with relative standard deviation values below 2.85%. The validated method was successfully applied to determine the contents of seven flavones in Juglandis Mandshuricae Cortex from seven sources and the contents of these places were calculated respectively. This method provides a theoretical basis for further developing the medicinal value of Juglandis Mandshuricae Cortex. 相似文献
4.
In [3], Poonen and Slavov recently developed a novel approach to Bertini irreducibility theorems over an arbitrary field, based on random hyperplane slicing. In this paper, we extend their work by proving an analogous bound for the dimension of the exceptional locus in the setting of linear subspaces of higher codimensions. 相似文献
5.
Large amounts of flowback and produced water (FPW) have been generated from hydraulic fracturing process for the production of unconventional gas such as shale gas. Complex organic pollutants are abundantly present in FPW with revealed toxicity to aquatic organisms and these contaminants may transfer into surrounding aquatic environment. Characterization and determination of complicated organic pollutants in FPW remains a challenge due to its complex composition and high salinity matrix. This review article covers the progress of recent 5 years regarding the sample preparation and instrumental analysis methods and thus summarizes the advantages and disadvantages of these methods for critical analysis of organic contaminants in FPW samples. Furthermore, the natural distribution of detected organic compounds and their transformation were reviewed and discussed to enhance the understanding of spatial and temporal behaviors of these organic pollutants in natural environment, paving the way for future development of pollution control policies and strategies. Enlightened by the studies of FPW contamination in the US, the investigations of FPW contamination in China continued to grow due to rapidly growing production of shale gas in China and resulted pollution. 相似文献
6.
7.
8.
9.
10.
Thermoelectric(TE)energy harvesting can effectively convert waste heat into electricity,which is a crucial technology to solve energy concerns.As a promising candidate for energy conversion,poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)has gained significant attention owing to its easy doping,high transparency,and solution processability.However,the TE performance of PEDOT:PSS still needs to be further enhanced.Herein,different approaches have been applied for tuning the TE properties:(i)direct dipping PEDOT:PSS thin films in ionic liquid;(ii)post-treatment of the films with concentrated sulfuric acid(H2SO4),and then dipping in ionic liquid.Besides,the same bis(trifluoromethanesulfonyl)amide(TFSI)anion and different cation salts,including 1-ethyl-3-methylimidazolium(EMIM+)and lithium(Li+),are selected to study the influence of varying cation types on the TE properties of PEDOT:PSS.The Seebeck coefficient and electrical conductivity of the PEDOT:PSS film treated with H2SO4EMIM:TFSI increase simultaneously,and the resulting maximum power factor is 46.7μW·m-1·K-2,which may be attributed to the ionic liquid facilitating the rearrangement of the molecular chain of PEDOT.The work provides a reference for the development of organic films with high TE properties. 相似文献