全文获取类型
收费全文 | 7774篇 |
免费 | 272篇 |
国内免费 | 13篇 |
专业分类
化学 | 4854篇 |
晶体学 | 147篇 |
力学 | 231篇 |
数学 | 770篇 |
物理学 | 2057篇 |
出版年
2023年 | 54篇 |
2022年 | 139篇 |
2021年 | 142篇 |
2020年 | 158篇 |
2019年 | 169篇 |
2018年 | 167篇 |
2017年 | 210篇 |
2016年 | 302篇 |
2015年 | 206篇 |
2014年 | 305篇 |
2013年 | 587篇 |
2012年 | 513篇 |
2011年 | 542篇 |
2010年 | 348篇 |
2009年 | 312篇 |
2008年 | 403篇 |
2007年 | 344篇 |
2006年 | 248篇 |
2005年 | 288篇 |
2004年 | 211篇 |
2003年 | 207篇 |
2002年 | 190篇 |
2001年 | 83篇 |
2000年 | 82篇 |
1999年 | 57篇 |
1998年 | 61篇 |
1997年 | 67篇 |
1996年 | 64篇 |
1995年 | 44篇 |
1994年 | 50篇 |
1993年 | 66篇 |
1992年 | 66篇 |
1991年 | 52篇 |
1990年 | 56篇 |
1989年 | 68篇 |
1988年 | 64篇 |
1987年 | 56篇 |
1986年 | 49篇 |
1985年 | 77篇 |
1984年 | 84篇 |
1983年 | 54篇 |
1982年 | 59篇 |
1981年 | 67篇 |
1980年 | 63篇 |
1979年 | 61篇 |
1978年 | 61篇 |
1977年 | 75篇 |
1976年 | 66篇 |
1975年 | 60篇 |
1974年 | 51篇 |
排序方式: 共有8059条查询结果,搜索用时 15 毫秒
961.
Vishnu J. Ram D. A. Vanden Berghe A. J. Vlietinck 《Journal of heterocyclic chemistry》1988,25(1):217-219
Reactions of 5-dimethylaminomethylene-6-imino-1,3-dimethyluracil hydrochloride (1) with active methylene compounds 2 and 4 yielded bi- and tricyclic heterocyclic compounds 3 and 5 . All the prepared compounds were screened for chemotherapeutical activities but none were active. 相似文献
962.
R.P. Rastogi Ram Shabd B.M. Upadhyay S.B. Singh P.C. Pandey 《Journal of membrane science》1984,19(1):51-73
Photoinduced potentials and currents and photo-electroosmotic velocities were measured across cellulose acetate membranes impregnated with chlorophyll pigments. Chlorophyll was extracted by both solvent extraction, Chls, and column chromatography, Chl. Photoelectric effects in membranes prepared with the following pigments were investigated: (i) Chls-a + β-carotene, (ii) Chls-b + xanthophyll, (iii) Chls-a, (iv) Chls-b, (v) β-carotene, (vi) xanthophyll, (vii) Chls-a + anthraquinone, (viii) Chls-b + anthraquinone, (ix) Chl-a, (x) Chl-b, (xi) Chl-a + anthraquinone, (xii) Chl-b + anthraquinone, (xiii) Chl-a + benzoquinone, and (xiv) Chl-b + benzoquinone. β-Carotene, xanthophyll, Chl-a and Chl-b obrained by chromatographic separation do not show a photoinduced potential or current. However, these effects are observed when “pure” (doubly chromatographed) Chl-a or Chl-b are mixed with anthraquinone or benzoquinone. These effects are observed in systems (i), (ii), (iii), (iv), (vii) and (viii) involving Chs. Although photoinduced potentials and photoinduced currents are not observed in Chl-a or Chl-b membranes, photoelectroosmosis is still observed. p]Both photoinduced potentials and currents are found to depend on pH. When the pH is changed appropriately, Chls-a acts as photocathode while Chls-b becomes a photoanode. Photocurrents are considerably enhanced when the pH is lowered. The change of photopotential with temperature is found to be insignificant. Photoelectroosmosis is always found to be directed towards the dark side, regardless of the polarity of the electrodes. A model based on the role of plastiquinone has been proposed to explain these phenomena, which have excellent reproducibility. The model predicts that ΔpH = (pH)d — (PH)1 (where (pH)d and (pH)1 denote the pH on the dark and illuminated side of the membrane respectively) would be positive when the pH of the bathing solution is higher than approximately 7, while it would be negative for lower pH. This behaviour is observed in the case of mixture of pure Chl-a + anthraquinone and pure Chl-b + benzoquinone. The model also predicts photoelectroosmosis irrespective of the presence of plastiquinone, in agreement with experimental observation. 相似文献
963.
Chemical correlation studies and application of Horeau's method establish the absolute stereochemistry of the major cadinene from . as shown in {=1}. 相似文献
964.
965.
966.
967.
Two approximations, the single super chainf-expansion (sscf), and Percus-Yevick (py) approximation, are evaluated for a molecular fluid in which the molecules interact with a pair potential, that is the sum
of Lennard-Jones and quadrupole-quadrupole parts at two values of reduced quadrupole moment. These results are compared with
Monte-Carlo results. Except for the harmonic coefficienth (222;r), thesscf approximation seems to be quite accurate for the lower value of quadrupole moment but at higher valuespy approximation produces much better results except forh(220;r). 相似文献
968.
969.
The results of a Compton profile study on polycrystallineα-Mn are reported. Our measurement are compared with theoretical results computed for different 3d-4s electron configurations within the RFA model. Best agreement between the measured and calculated values is found for 3d
5·44s
1·6 configuration. Theoretical Compton profile ofγ-Mn calculated using the same procedure is close to that for bcc phase with similar electron configurations. 相似文献
970.
A simple, accurate and reliable titrimetric method is described for the determination of thiophanate-methyl, an important commercial fungicide. The method is based on its direct titration at room temperature with ammonium hexanitratocerate(IV) in sulphuric acid medium in the presence of potassium iodate as catalyst. The method permits detection of the end-point visually, potentiometrically or spectrophotometrically. The proposed method is recommended for routine determination of the fungicide in its commercial formulations. 相似文献