全文获取类型
收费全文 | 12497篇 |
免费 | 2156篇 |
国内免费 | 2265篇 |
专业分类
化学 | 10388篇 |
晶体学 | 186篇 |
力学 | 590篇 |
综合类 | 139篇 |
数学 | 1576篇 |
物理学 | 4039篇 |
出版年
2024年 | 9篇 |
2023年 | 160篇 |
2022年 | 270篇 |
2021年 | 329篇 |
2020年 | 399篇 |
2019年 | 523篇 |
2018年 | 415篇 |
2017年 | 440篇 |
2016年 | 588篇 |
2015年 | 703篇 |
2014年 | 784篇 |
2013年 | 986篇 |
2012年 | 1177篇 |
2011年 | 1194篇 |
2010年 | 906篇 |
2009年 | 903篇 |
2008年 | 1023篇 |
2007年 | 861篇 |
2006年 | 776篇 |
2005年 | 746篇 |
2004年 | 615篇 |
2003年 | 431篇 |
2002年 | 494篇 |
2001年 | 396篇 |
2000年 | 303篇 |
1999年 | 234篇 |
1998年 | 183篇 |
1997年 | 170篇 |
1996年 | 154篇 |
1995年 | 133篇 |
1994年 | 125篇 |
1993年 | 91篇 |
1992年 | 67篇 |
1991年 | 73篇 |
1990年 | 64篇 |
1989年 | 41篇 |
1988年 | 44篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1965年 | 3篇 |
1939年 | 1篇 |
1936年 | 8篇 |
1935年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Copper‐Catalyzed Difunctionalization of Activated Alkynes by Radical Oxidation–Tandem Cyclization/Dearomatization to Synthesize 3‐Trifluoromethyl Spiro[4.5]trienones 下载免费PDF全文
Dr. Hui‐Liang Hua Yu‐Tao He Yi‐Feng Qiu Ying‐Xiu Li Bo Song Pin Gao Xian‐Rong Song Dong‐Hui Guo Prof. Dr. Xue‐Yuan Liu Prof. Dr. Yong‐Min Liang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1468-1473
A copper‐catalyzed difunctionalizing trifluoromethylation of activated alkynes with the cheap reagent sodium trifluoromethanesulfinate (NaSO2CF3 or Langlois’ reagent) has been developed incorporating a tandem cyclization/dearomatization process. This strategy affords a straightforward route to synthesis of 3‐(trifluoromethyl)‐spiro[4.5]trienones, and presents an example of difunctionalization of alkynes for simultaneous formation of two carbon–carbon single bonds and one carbon–oxygen double bond. 相似文献
92.
93.
94.
95.
In this study, we present a method to predict the droplet ejection in thermal inkjet printheads including the growth and collapse of a vapor bubble and refill of the firing chamber. The three‐dimensional Navier–Stokes equations are solved using a finite‐volume approach with a fixed Cartesian mesh. The piecewise‐linear interface calculation‐based volume‐of‐fluid method is employed to track and reconstruct the ink–air interface. A geometrical computation based on Lagrangian advection is used to compute the mass flux and advance the interface. A simple and efficient model for the bubble dynamics is employed to model the effect of ink vapor on the adjacent ink liquid. To solve the surface tension‐dominated flow accurately, a hierarchical curvature‐estimation method is proposed to adapt to the local grid resolution. The numerical methods mentioned earlier have been implemented in an internal simulation code, CFD3. The numerical examples presented in the study show good performance of CFD3 in prediction of surface tension‐dominated free‐surface flows, for example, droplet ejection in thermal inkjet printing. Currently, CFD3 is used extensively for printhead development within Hewlett‐Packard. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
96.
97.
Shu-jie Miao Yun-fa Qiao Meng-yang You Fu-tao Zhang 《Journal of Thermal Analysis and Calorimetry》2016,123(3):2045-2051
Long-term continuous cropping affects the biochemical quality of soil organic matter (SOM), but whether the effects are relevant with their thermal stability is less clear. In northeast China, long-term continuous cropping occurred frequently owing to higher yield and economic interest requirement. To verify the thermal stability properties of SOM affected by the long-term continuous cropping, the study focused on 23-yr continuous cultivated maize and soybean plots, where the effect of cropping is likely to be detected. Bulk soils sampled in 1991 and 2014 were studied by thermogravimetry and differential scanning calorimetry (DSC). The results showed typical bimodal peaks in DSC curve in bulk Mollisols. A labile fraction peak was observed at 354–366 °C low-temperature zone and recalcitrant fraction one at high temperature of 430–438 °C. Energy density (J mg?1 OM) was greater in soybean plots compared to maize plots; in contrast, long-term continuous maize cultivation also increased energy density, in reverse in soybean plots after 23-yr cultivation. The DSC-T50, temperature at which half of energy release occurred, typically showed larger responses to long-term cultivation than crop species. Results obtained support the hypothesis of a potential link between long-term continuous cropping and the thermal stability of SOM, and a correlation with crop species. 相似文献
98.
99.
100.
Yan Wu Yimin Yang Hua Wang Changsui Wang 《Applied Physics A: Materials Science & Processing》2014,114(2):503-507
Different types of phytolith even when coming from the same plant react to high temperatures in different ways. To understand the behavior of phytoliths upon heating, we examined composition and distribution of some elements within different phytolith types using SEM-EDS and synchrotron radiation μ-X-ray fluorescence. By analyzing phytoliths from rice husk, rice leaf and Than tree leaf, we find that the compositions and distributions of metal oxides within different phytolith types are quite different. It is well known that metal oxides have been used as fluxing agent to reduce the melting temperature of SiO2 in the production of glass, and different metal oxides can be used to produce a variety of glass with diverse features. Similarly, metal elements including potassium, magnesium and calcium in phytoliths should also act as a fluxing agent under high temperature, and the differential compositions and distributions of these metal elements within the phytoliths resulted in the variable reaction to heating. In sum, there is a negative relationship between the flux elements composition in phytoliths, and the temperatures at which phytoliths deform; furthermore, potassium and calcium in the rice leaf phytolith are almost evenly distributed in all parts, which may cause the phytolith’s shape to deform evenly. In comparison, Than tree leaf phytolith is found to have a high percentage of potassium and calcium located exclusively on the outside, which may explain why the deformation of Than tree leaf phytolith occurs firstly at the outside. 相似文献