全文获取类型
收费全文 | 29658篇 |
免费 | 135篇 |
国内免费 | 284篇 |
专业分类
化学 | 11032篇 |
晶体学 | 269篇 |
力学 | 1414篇 |
综合类 | 12篇 |
数学 | 9151篇 |
物理学 | 8199篇 |
出版年
2022年 | 51篇 |
2021年 | 74篇 |
2020年 | 41篇 |
2019年 | 38篇 |
2018年 | 1204篇 |
2017年 | 1458篇 |
2016年 | 749篇 |
2015年 | 583篇 |
2014年 | 507篇 |
2013年 | 707篇 |
2012年 | 3174篇 |
2011年 | 2368篇 |
2010年 | 1812篇 |
2009年 | 1561篇 |
2008年 | 599篇 |
2007年 | 658篇 |
2006年 | 640篇 |
2005年 | 4456篇 |
2004年 | 3939篇 |
2003年 | 2330篇 |
2002年 | 494篇 |
2001年 | 304篇 |
2000年 | 102篇 |
1999年 | 180篇 |
1998年 | 115篇 |
1997年 | 71篇 |
1996年 | 57篇 |
1995年 | 49篇 |
1994年 | 54篇 |
1992年 | 177篇 |
1991年 | 164篇 |
1990年 | 146篇 |
1989年 | 116篇 |
1988年 | 106篇 |
1987年 | 62篇 |
1986年 | 45篇 |
1985年 | 44篇 |
1984年 | 38篇 |
1983年 | 32篇 |
1979年 | 32篇 |
1976年 | 80篇 |
1975年 | 39篇 |
1974年 | 42篇 |
1973年 | 49篇 |
1972年 | 39篇 |
1970年 | 34篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1967年 | 30篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Florence Geneste Alec Moradpour Georges Dive Daniel Peeters Jacques Malthête Jean-Fran?ois Sadoc 《The Journal of organic chemistry》2002,67(2):605-607
The total number of possible retrosynthetic bisections of C(60) leads to nine different isometric C(30) fragments. These molecules include five chiral units, four of which derive from partitions corresponding to four distinct "Coupes du Roi". The energies, curvatures, and homodesmotic stabilization energies of the C(30) fragments are evaluated at the ab initio 6-31G level. 相似文献
993.
Zbigniew GrobelnyAndrzej Stolarzewicz Barbara Morejko-Bu?Adalbert Maercker 《Journal of organometallic chemistry》2002,660(1):6-13
The linear ether bond was exclusively cleaved in benzyl glycidyl ether and triphenylmethyl glycidyl ether under the influence of K−, K+(15-crown-5)2 (1), whereas the strongly strained three-membered oxacyclic ring remained undisturbed. Potassium glycidoxide and benzylpotassium were found as the primary reaction products of benzyl glycidyl ether with 1. Subsequently, benzylpotassium reacted with benzyl glycidyl ether giving the next potassium glycidoxide molecule and bibenzyl. Benzyl phenyl ether was used as a model compound to explain the mechanism of bibenzyl formation. The reaction of triphenylmethyl glycidyl ether with 1 resulted in potassium glycidoxide and stable triphenylmethylpotassium. After treating with a quenching agent a new glycidyl ether or glycidyl ester was obtained from potassium glycidoxide. These results were found when the reaction occurred at the excess of glycidyl ether. In another case, i.e. at the excess of 1 further reactions took place with the participation of potassium anions and various new compounds were observed in the reaction mixture after benzylation or methylation. Thus, the method of substrates delivery influences the course of studied processes in a decisive way. 相似文献
994.
995.
996.
997.
Koziołkiewicz M Owczarek A Wójcik M Domański K Guga P Stec WJ 《Journal of the American Chemical Society》2002,124(17):4623-4627
A new method of analysis has allowed the exonucleolytic cleavage by human 3'-exonuclease to be determined. Hydrolysis by human plasma 3'-exonuclease proceeds with retention of configuration at phosphorus. The new method determines the sense of chirality at phosphorus in isotopomeric adenosine 5'-O-[(18)O]phosphorothioates. This is based on stereospecific two-step conversion of the mono-thionucleotide into the corresponding deoxyadenosine 5'-O-alpha-[(18)O]thiotriphosphate, followed by the use of terminal deoxyribonucleotidyl transferase and MALDI TOF mass spectrometry of the resulting elongated primer. Retention of configuration in the reaction of plasma 3'-exonuclease implies a two-step mechanism with two displacements on phosphorus. Inversion at each step leads to overall retention. 相似文献
998.
Magnetic metal and metal oxide nanoparticles capped with alkylamines have been synthesized and characterized by transmission
electron microscopy. X-ray diffraction, energy dispersive X-ray analysis and magnetization measurements. Core-shell Pd-Ni
particles with composition, Pd561Ni3000, (diameter ∼3.3 nm) are superparamagnetic at 5 K and organize themselves into two-dimensional crystalline arrays. Similar
arrays are obtained with Pd561Ni3000Pd1500 nanoparticles containing an additional Pd shell. Magnetic spinel particles of γ-Fe2O3, Fe3O4 and CoFe2O4 of average diameters in the 4–6 nm range coated with octylamine are all supermagnetic at room temperature and yield close-packed
disordered arrays. Relatively regular arrays are formed by dodecylaminecapped Fe3O4 nanoparticles (∼8.6 nm diameter) while well-ordered hexagonal arrays were obtained with octylamine-covered Co3O4 nanoparticles (∼4.2 nm diameter). 相似文献
999.
Background
The mechanism of aluminum-induced neurotoxicity is not clear. The involvement of glutamate in the aluminium-induced neurocomplications has been suggested. Brain glutamate levels also found to be altered in protein malnutrition. Alterations in glutamate levels as well as glutamate-α-decarboxylase in different regions of rat brain has been reported in response to aluminum exposure. Thus the study of glutamate metabolising enzymes in different brain regions of rats maintained on either normal or restricted protein diet may be of importance for understanding the neurotoxicity properties of aluminium. 相似文献1000.
Wojciech Czardybon Wojciech Sokol John Warkentin Nick Henry Werstiuk 《Journal of Physical Organic Chemistry》2008,21(1):41-46
Synthesis of a bicyclic 2,2‐dioxa oxadiazoline (6,7‐diaza‐1‐methoxy‐5‐methyl‐2,8‐dioxabicyclo[3.2.1]oct‐6‐ene) is reported. Its thermolysis at 27°C is about 200 times as fast as the thermolysis of a monocyclic oxadiazoline model system. Presumably, a cyclic dioxa carbonyl ylide is formed initially and the ylide then undergoes a bond scission to afford either a dioxacarbene or a dialkylcarbene or it cyclizes to an oxirane. A small fraction of a dialkylcarbene was trapped as the product of addition to dimethyl acetylenedicarboxylate (DMAD). Computations of the barriers to the loss of N2 from the oxadiazolines and to the formation of the carbenes from the carbonyl ylide resulting from thermolysis of the bicyclic oxadiazoline are compared to corresponding barriers for a similar monocyclic oxadiazoline. The rate acceleration is accounted for in terms of geometric factors. The complex products from the decomposition of the bicyclic oxadiazoline were not studied. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献