全文获取类型
收费全文 | 14252篇 |
免费 | 2782篇 |
国内免费 | 2493篇 |
专业分类
化学 | 11149篇 |
晶体学 | 314篇 |
力学 | 710篇 |
综合类 | 170篇 |
数学 | 1328篇 |
物理学 | 5856篇 |
出版年
2024年 | 35篇 |
2023年 | 300篇 |
2022年 | 433篇 |
2021年 | 627篇 |
2020年 | 732篇 |
2019年 | 726篇 |
2018年 | 600篇 |
2017年 | 618篇 |
2016年 | 806篇 |
2015年 | 844篇 |
2014年 | 1062篇 |
2013年 | 1318篇 |
2012年 | 1506篇 |
2011年 | 1527篇 |
2010年 | 1115篇 |
2009年 | 1022篇 |
2008年 | 1156篇 |
2007年 | 920篇 |
2006年 | 812篇 |
2005年 | 632篇 |
2004年 | 511篇 |
2003年 | 369篇 |
2002年 | 312篇 |
2001年 | 258篇 |
2000年 | 214篇 |
1999年 | 195篇 |
1998年 | 141篇 |
1997年 | 93篇 |
1996年 | 111篇 |
1995年 | 84篇 |
1994年 | 79篇 |
1993年 | 71篇 |
1992年 | 53篇 |
1991年 | 55篇 |
1990年 | 32篇 |
1989年 | 33篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 29篇 |
1985年 | 20篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1959年 | 1篇 |
1957年 | 5篇 |
1937年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
Uncoupled metabolism stimulated by chemical uncoupler and oxic-settling-anaerobic combined process to reduce excess sludge production 总被引:1,自引:0,他引:1
The effects of three uncoupled metabolic systems (conventional activated sludge process with the addition of 3,3′,4′,5-tetrachlorosalicylanilide
[TCS], oxic-settling-anaerobic [OSA] process modified by insertion of a sludge-holding tank in the sludge return line, and
TCS and OSA combined process) on reducing excess sludge production were studied. Compared with the control conventional activated
sludge process, the most effective system was the combined process, which could reduce excess sludge production by 46.90%.
The 180-d operation results confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield but that it
had an adverse effect on substrate removal capability, effluent nitrogen concentration, and sludge settleability. The OSA
process decreased excess sludge production by only 26% but had less adverse effect on effluent quality and could improve sludge
settleability. The effluent total phosphorous concentration of the three systems was slightly lower than of the control unit.
Microbial populations were monitored by both microscopic and molecular biologic analysis method (polymerase chain reaction
[PCR]-denaturing gradient gel electrophoresis [DGGE]). The presence of TCS caused metazoans to disappear and decreased the
number and activity of protozoa. PCR amplification of 16S rRNA and sequent DGGE analysis found a shift in the diversity of
the predominant species. The results imply that OSA combined with the chemical uncoupler process may effectively reduce excess
sludge yield and not affect process performance significantly. 相似文献
154.
用量子化学从头算方法 ,在RHF/STO - 3G水平上 ,对 2_三氰基乙烯基蒽 (2_TCVA)分子进行了理论计算 ,优化得到了它的平衡几何构型 ,并计算了它的谐振动频率 .结果表明 :2_TCVA存在两种旋转异构体 :2_TCVA(1)和 2_TCVA(2 ) ,2_TCVA(2 )的总能量比 2_TCVA(1)的略高 .在PM3/CIS水平上计算了它们的电子光谱 ,得到了由基态到各激发态的垂直跃迁能和相应的振子强度 .研究表明 :2_TCVA(1)和 2_TCVA(2 )的强度最大的吸收波长分别为 2 4 9.72nm和 2 89.4 1nm ,2_TCVA(2 )的强度最大的吸收波长比 2_TCVA(1)的要长 .计算结果与实验结果符合得较好 相似文献
155.
Rong-Min Wang Zong-Fan Duan Yu-Feng He Zi-Qiang Lei 《Journal of molecular catalysis. A, Chemical》2006,260(1-2):280-287
A new kind of Co–Na heterodinuclear polymer complex based on Salen Schiff base and crown ether has been successfully prepared by condensation polymerization. Its catalytic behavior for aerobic oxidation of cyclohexene, alkylbenzenes and linear aliphatic olefins was studied in the absence of any solvents or reducing agents under mild conditions. The oxidation of cyclohexene catalyzed by the above catalyst proved to be a simple and efficient method for obtaining 2-cyclohexen-1-one (CO) and 2-cyclohexen-ol (OH) in a high selectivity. Kinetics of the oxidation was also investigated. The results showed that the aerobic oxidation of cyclohexene catalyzed by Salen-crown ether heterodinuclear polymer complex follows a radical chain aerobic oxidation mechanism. This oxidation system is also efficient in the oxidation of alkylbenzenes and linear aliphatic olefins, which afforded corresponding benzylic oxidation products and epoxides, respectively. 相似文献
156.
157.
158.
159.
Lei Qiao Chao Zhang Xiang‐Wen Zhang Zi‐Chuan Wang Haolin Yin Zhong‐Ming Sun 《中国化学》2020,38(3):295-304
The polypnictide complexes of rare earth cations have drawn the attention of the scientific community for their uncommon bonding modes and potential applications. Herein, we present a systematic and comprehensive summary on recent advances in the field of rare earth polypnictides, focusing on their synthesis, structures, and reactivities. The structural stabilizing effects imposed by the electropositive rare earth cations as well as the reducing capability of rare earth precursors in the synthesis of these polypnictide complexes are described in this review. We also disscuss in detail the bonding interactions and coordination modes between rare earth cations and polypnictide clusters as well as the similarities and the peculiarity of some structures. 相似文献
160.