全文获取类型
收费全文 | 3251篇 |
免费 | 531篇 |
国内免费 | 335篇 |
专业分类
化学 | 2129篇 |
晶体学 | 34篇 |
力学 | 260篇 |
综合类 | 27篇 |
数学 | 386篇 |
物理学 | 1281篇 |
出版年
2024年 | 4篇 |
2023年 | 71篇 |
2022年 | 120篇 |
2021年 | 143篇 |
2020年 | 140篇 |
2019年 | 124篇 |
2018年 | 103篇 |
2017年 | 103篇 |
2016年 | 176篇 |
2015年 | 164篇 |
2014年 | 205篇 |
2013年 | 235篇 |
2012年 | 318篇 |
2011年 | 321篇 |
2010年 | 224篇 |
2009年 | 222篇 |
2008年 | 202篇 |
2007年 | 183篇 |
2006年 | 179篇 |
2005年 | 142篇 |
2004年 | 117篇 |
2003年 | 79篇 |
2002年 | 69篇 |
2001年 | 64篇 |
2000年 | 48篇 |
1999年 | 68篇 |
1998年 | 42篇 |
1997年 | 37篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 25篇 |
1993年 | 21篇 |
1992年 | 20篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 3篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4117条查询结果,搜索用时 15 毫秒
51.
液相色谱中一个新的表征参数Z:Ⅱ.反相液相色谱中小分子极性溶质体系 总被引:3,自引:2,他引:3
反相高效液相色谱(RPLC)中小分子极性溶质的极性是可以用液相色谱中溶质计量置换保留模型中的Z值(1mol溶质被固定相吸附时,在固定相与溶质子间释放出置换剂的mol数)来表征的,其大小可用带有该极性端基的同系物的Z值对碳原子数线性作图的截距求得。这些检性基的Z测量定值与疏水性片段指数1gf间有极好的线性关系。依此关系还可测出一些用其他实验方法无法测得的某些基团的1gf值。 相似文献
52.
A parallel solution combustion synthesis technique was developed for combinatorial materials studies. The vigorous combustion reactions were successfully limited in the microreactors by using a substrate-net-mask microreactor system and the lowest adoptable furnace temperature. Using this technique, a luminescent materials library of Y3Al5O12/Tb(chi) was synthesized with the aid of an ink-jet delivery system. Structure and luminescence characterizations were implemented using X-ray diffraction and UV/X-ray spectroscopies, respectively. The results show that this technique is reliable and applicable to combinatorial study of powder materials with high synthesis temperature. 相似文献
53.
Dudkin VY Orlova M Geng X Mandal M Olson WC Danishefsky SJ 《Journal of the American Chemical Society》2004,126(31):9560-9562
Synthetic gp120331-335 glycopeptide fragments carrying hybrid and high-mannose type N-linked glycans were evaluated for binding to broadly neutralizing antibody 2G12 using surface plasmon resonance technology. None of the hybrid-type constructs demonstrated binding to 2G12. In the high-mannose series, the "Cys dimer" construct, presenting two undecasaccharide glycans, showed significantly higher binding than the Cys-protected monomer. The binding of the dimeric structure was further investigated in competition with recombinant gp120. The data suggest that gp120 and its designed synthetic epitope construct bind to the same site on 2G12. 相似文献
54.
Li Yan Liang Shao Ping Ren Yi Quan Zheng Man Geng Lu Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Key Laboratory of Polymer Materials for Electronics Guangdong China Graduate School of the Chinese Academy of Sciences Beijing China 《中国化学快报》2007,18(2):225-228
A series of novel liquid crystalline epoxides with lateral substituents were cured with anhydrides and the cure kinetics was investigated by non-isothermal DSC technique. The results showed that the lengths of lateral substituents have great effect on the value of Ea. The curing reaction became less active, when the liquid crystalline epoxides have long lateral substituents and were controlled by diffusion at the late stage of cure. A nematic structure was observed by POM and XRD. 相似文献
55.
An oligosaccharide homologue named SnS-2 was isolated from the root of Scrophularia ningpoensis Hemsl.SnS-2 was purified by means of gel-permeation chromatography and ion-exchange chromatography. Its physicochemical properties, including carbohydrate content and molecular weight were determined. The structure of SnS-2 was elucidated by chemical methods along with ^1H and ^13C NMR spectroscopy, including two-dimensional DQCOSY and H-detected ^1H, ^13C HMQC experiments. These results show that SnS-2 possesses a backbone consisting of terminal α-Galp-(1→, α-Galp-(1→6), α-Glcp-(1→6) and nonreducing end β-Fruf-(2→. The bioactive assay showed that it could inhibit the growth of Lewis pulmonary carcinoma implanted in mice. 相似文献
56.
流动注射—化学发光法测定苯甲醛 总被引:1,自引:0,他引:1
依据苯甲醛增强没食子酸-过氧化氢-氢氧化钠体系化学发光的性质,建立了苯甲醛的流动注射化学发光分析法。 相似文献
57.
David Zhigang Wang 《Tetrahedron》2005,61(30):7134-7143
In the framework of a helix theory recently developed for molecular chiralities and chiral interactions, it is further proposed that for an asymmetric reaction to be highly enantioselective, the helical characters, that is, the local energies of electrons on the helices, of the catalyst and the substrate complexed with it in the corresponding enantioselection-determining step must be matched. These helical characters can be analyzed on the basis of molecular polarizability and structure properties under a given reaction mechanism. This proposal highlights the importance of polarizability matching in three-dimension chiral space and in essence is a chiral version of the classical hard and soft acid-base theory. It also from an electronic effect angle sheds light on the nature of the conventional lock-and-key origin of high enantioselection and carries the message that, to design a good catalyst (the key), rather than focusing on the rigidity, bulkiness or C2-symmetry of the catalyst, one should focus more on the helical character of the substrate (the lock) with which the catalyst will interact. It is generally easier to discover a highly enantioselective catalyst for a substrate of a large helical character than for a substrate of a small helical character. The proposal is supported by theoretical modeling as well as numerous experiments and is used to understanding various aspects of current asymmetric catalysis. 相似文献
58.
59.
60.