全文获取类型
收费全文 | 19685篇 |
免费 | 2802篇 |
国内免费 | 1052篇 |
专业分类
化学 | 21764篇 |
晶体学 | 64篇 |
力学 | 36篇 |
综合类 | 17篇 |
数学 | 22篇 |
物理学 | 1636篇 |
出版年
2024年 | 20篇 |
2023年 | 264篇 |
2022年 | 556篇 |
2021年 | 695篇 |
2020年 | 1274篇 |
2019年 | 975篇 |
2018年 | 796篇 |
2017年 | 665篇 |
2016年 | 1280篇 |
2015年 | 1104篇 |
2014年 | 1201篇 |
2013年 | 1460篇 |
2012年 | 1133篇 |
2011年 | 1292篇 |
2010年 | 1070篇 |
2009年 | 1145篇 |
2008年 | 1065篇 |
2007年 | 1016篇 |
2006年 | 927篇 |
2005年 | 858篇 |
2004年 | 833篇 |
2003年 | 624篇 |
2002年 | 1272篇 |
2001年 | 309篇 |
2000年 | 195篇 |
1999年 | 228篇 |
1998年 | 260篇 |
1997年 | 192篇 |
1996年 | 142篇 |
1995年 | 125篇 |
1994年 | 71篇 |
1993年 | 65篇 |
1992年 | 53篇 |
1991年 | 39篇 |
1990年 | 44篇 |
1989年 | 23篇 |
1988年 | 30篇 |
1987年 | 24篇 |
1986年 | 68篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1973年 | 7篇 |
1972年 | 11篇 |
1970年 | 7篇 |
1966年 | 9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.
Susana Conde Ceide 《Tetrahedron letters》2006,47(26):4415-4418
We herein report that flash heating microwave irradiation is a helpful tool in the formation of arylpyrimidines from the corresponding halopyrimidines. The palladium-catalyzed cross-coupling reactions of 2,4-di- and 2,4,5-trihalopyrimidines with phenylboronic acid under the above conditions are described. By use of the appropriate catalyst and the adequate halopyrimidine, good regioselectivity can be achieved in the 2-, 4-, or 5-positions of the heterocycle. In addition, we show that this methodology is ameneable for the stepwise preparation of mono-, di-, and triphenylpyrimidines. 相似文献
37.
空心阴极灯激发的微波等离子体炬原子/离子荧光光谱研究--钙的原子/离子荧光光谱 总被引:2,自引:0,他引:2
用强短脉冲供电技术的空心阴极灯作激发源、微波等离子体炬作原子/离子化器,建立了原子/离子荧光光谱实验装置。详细研究了微波等离子体功率、观察高度、空心阴极灯电流等因素对原子/离子荧光信号强度的影响,测量了系统对Ca的原子/离子荧光光谱的检出限。 相似文献
38.
The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm2 range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction. 相似文献
39.
Jesús Vázquez 《Tetrahedron letters》2006,47(10):1657-1661
Use of a semicarbazide resin for the solid-phase preparation of peptide ketones and aldehyde led to optimal results in terms of both purity of the final product and overall yield. This resin was prepared without complication by activation of the commercial available aminomethyl polystyrene with CDI at room temperature, followed by treatment with tert-butyl carbazate. Furthermore, the TNBSA colorimetric assay has been adapted for checking the incorporation of the carbonyl moiety onto hydrazine-based resins. 相似文献
40.
The rotational spectra of the deuterium cyanide isotopic species DCN, D13CN, DC15N, and D13C15N were recorded in the vibrational ground and first excited bending state (v2=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the 14N nucleus in DCN and D13CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D13C15N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the 14N nucleus for DCN and D13CN. The hyperfine structure due to the D, 13C, and 15N nuclei have not been resolved, but led to a broadening of the observed saturation dips. 相似文献