全文获取类型
收费全文 | 1211篇 |
免费 | 99篇 |
国内免费 | 4篇 |
专业分类
化学 | 1051篇 |
晶体学 | 13篇 |
力学 | 15篇 |
数学 | 68篇 |
物理学 | 167篇 |
出版年
2023年 | 15篇 |
2022年 | 19篇 |
2021年 | 29篇 |
2020年 | 31篇 |
2019年 | 27篇 |
2018年 | 35篇 |
2017年 | 19篇 |
2016年 | 55篇 |
2015年 | 43篇 |
2014年 | 68篇 |
2013年 | 70篇 |
2012年 | 108篇 |
2011年 | 152篇 |
2010年 | 70篇 |
2009年 | 65篇 |
2008年 | 97篇 |
2007年 | 74篇 |
2006年 | 68篇 |
2005年 | 54篇 |
2004年 | 54篇 |
2003年 | 44篇 |
2002年 | 34篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1314条查询结果,搜索用时 500 毫秒
141.
Ultrafast internal conversion of benzene and toluene from the S(2) states was studied by time-resolved photoelectron imaging with a time resolution of 22 fs. Time-energy maps of the photoelectron intensity and the angular anisotropy were generated from a series of photoelectron images. The photoelectron kinetic energy distribution exhibits a rapid energy shift and intensity revival, which indicates nuclear motion on the S(2) adiabatic surface, while the ultrafast evolution of the angular anisotropy revealed a change in the electronic character of the S(2) adiabatic surface. From their decay profiles of the total photoelectron intensity, the time constants of 48 ± 4 and 62 ± 4 fs were determined for the population decay from the S(2) states in benzene and toluene, respectively. 相似文献
142.
Terai T Maki E Sugiyama S Takahashi Y Matsumura H Mori Y Nagano T 《Chemistry & biology》2011,18(10):1261-1272
Biotin-(strept)avidin complex is widely used in biotechnology because of its extremely high binding constant, but there is no report describing spatiotemporally controlled formation of the complex in live cells. Here, based on X-ray crystal structure analysis and calorimetric data, we designed and synthesized photoreleasable biotins, which show greatly reduced affinity for (strept)avidin, but recover native affinity after UV irradiation. For application at the cell surface, we introduced an amine-reactive moiety into these "caged" biotin molecules. Specific fluorescence imaging of live cells that had been labeled with these agents and then UV-irradiated, was accomplished by addition of streptavidin conjugated with a fluorophore. We also demonstrated the applicability of these compounds for UV-irradiated-cell-specific drug delivery by using caged-biotin-labeled cells, a prodrug, and streptavidin conjugated with a prodrug-activating enzyme. 相似文献
143.
Catalytic conversion of unreactive sp(3) C-O bonds in alkyl ethers to C-C bonds is described. Alkyl ethers bearing 2- or 4-pyridyl groups were coupled with triarylboroxines in the presence of a ruthenium catalyst. Triarylboroxines bearing a variety of functional groups including electron-withdrawing and -donating groups can be used for the reaction. No additional base was required for the coupling with the organoboron reagents, and base-sensitive groups can be tolerated. The reaction is considered to proceed via dehydroalkoxylation followed by addition of triarylboroxines to form C-C bonds. 相似文献
144.
A nickel-catalyzed cycloaddition has been developed where readily available anthranilic acid derivatives react with alkynes to afford substituted indoles. The reaction involves oxidative addition of Ni(0) to an ester moiety, which allows intermolecular addition to alkynes via decarbonylation and 1,3-acyl migration. 相似文献
145.
The decarbonylative cycloadditions of phthalic anhydrides with allenes were performed by using nickel catalyst. The asymmetric variant of the cycloaddition was also achieved by using chiral phosphine ligands to provide δ-lactones enantioselectively. 相似文献
146.
The dehydrogenative cycloaddition of dieneynes, which possess a diene in the form of a styrene moiety and a dienophile in the form of an alkyne moiety, produces naphthalene derivatives when heated. It was found that a key requirement of this process is the presence of a silyl group attached to the alkyne moiety, which forces a dehydrogenation reaction to occur. 相似文献
147.
Kitano H Suzuki H Kondo T Sasaki K Iwanaga S Nakamura M Ohno K Saruwatari Y 《Macromolecular bioscience》2011,11(4):557-564
A CMB monomer was polymerized on a glass plate with a surface-confined ATRP initiator containing a 2-bromoisobutyryl group. The glass plate modified with a PCMB brush was highly hydrophilic and showed a strong resistance against non-specific adsorption of proteins and cell adhesion. Upon ion beam irradiation, furthermore, the PCMB brush was ablated and a hollow space with a designed shape could be made to which HEK293 cells (from human embryonic kidney) and Hep G2 (from human hepatoma) cells non-specifically adhered, while no adhesion of these cells to the non-treated area on the brush was observed. The present results clearly indicate the usefulness of ion beam-printed patterns of anti-biofouling zwitterionic polymer brushes in the biomedical field. 相似文献
148.
A homology cylinder over a surface consists of a homology cobordism between two copies of the surface and markings of its
boundary. The set of isomorphism classes of homology cylinders over a fixed surface has a natural monoid structure and it
is known that this monoid can be seen as an enlargement of the mapping class group of the surface. We now focus on abelian
quotients of this monoid. We show that both the monoid of all homology cylinders and that of irreducible homology cylinders
are not finitely generated and moreover they have big abelian quotients. These properties contrast with the fact that the
mapping class group is perfect in general. The proof is given by applying sutured Floer homology theory to homologically fibered
knots studied in a previous paper. 相似文献
149.
Miyazaki M Ando N Sugai K Seito Y Fukuoka H Kanemitsu T Nagata K Odanaka Y Nakamura KT Itoh T 《The Journal of organic chemistry》2011,76(2):534-542
A catalytic asymmetric allylation of 3,4-dihydroisoquinoline was carried out with allyltrimethoxylsilane-Cu as the nucleophile in the presence of DTBM-SEGPHOS as the chiral ligand to afford corresponding chiral 1-allyltetrahydroisoquinoline derivatives in good yield and stereoselectivity. The allyl adduct thus obtained was applied to the synthesis of several isoquinoline alkaloids such as crispine A and homolaudanosine. The reaction was further used for the synthesis of the isoquinoline moiety of schulzeine A. 相似文献
150.
Horie H Koyama I Kurahashi T Matsubara S 《Chemical communications (Cambridge, England)》2011,47(9):2658-2660
The linear codimerization of acrylates and alkynes to produce 1,3-dienes is successfully demonstrated using a nickel catalyst in association with 2-aminopyridine as an additive. 相似文献