全文获取类型
收费全文 | 4540篇 |
免费 | 598篇 |
国内免费 | 442篇 |
专业分类
化学 | 3381篇 |
晶体学 | 50篇 |
力学 | 251篇 |
综合类 | 36篇 |
数学 | 487篇 |
物理学 | 1375篇 |
出版年
2024年 | 11篇 |
2023年 | 70篇 |
2022年 | 109篇 |
2021年 | 150篇 |
2020年 | 149篇 |
2019年 | 169篇 |
2018年 | 148篇 |
2017年 | 128篇 |
2016年 | 213篇 |
2015年 | 180篇 |
2014年 | 224篇 |
2013年 | 320篇 |
2012年 | 321篇 |
2011年 | 366篇 |
2010年 | 249篇 |
2009年 | 243篇 |
2008年 | 274篇 |
2007年 | 248篇 |
2006年 | 250篇 |
2005年 | 178篇 |
2004年 | 169篇 |
2003年 | 146篇 |
2002年 | 175篇 |
2001年 | 131篇 |
2000年 | 103篇 |
1999年 | 110篇 |
1998年 | 95篇 |
1997年 | 84篇 |
1996年 | 52篇 |
1995年 | 71篇 |
1994年 | 60篇 |
1993年 | 50篇 |
1992年 | 51篇 |
1991年 | 32篇 |
1990年 | 37篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 12篇 |
1986年 | 26篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1977年 | 4篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1969年 | 4篇 |
排序方式: 共有5580条查询结果,搜索用时 15 毫秒
991.
In the presence of graphene oxide, upon formation of cytosine-Ag-cytosine the fluorescence wavelength of FAM-labeled DNA exhibited a red shift, and its intensity significantly increased. A novel fluorescent DNA sensor for Ag(+) and cysteine detection, and a dual-output fluorescent DNA INHIBIT logic gate are designed. 相似文献
992.
J Shin NS Kang KH Kim TW Lee JI Jin M Kim K Lee BK Ju JM Hong DH Choi 《Chemical communications (Cambridge, England)》2012,48(68):8490-8492
A new anthracene-based X-shaped conjugated molecule, HBTATHT, was synthesized. Thin film transistors based on unannealed HBTATHT showed a carrier mobility of 0.15 cm(2) V(-1) s(-1) (I(on/off) = 7.9 × 10(6)). Further, a solution processed solar cell made of HBTATHT exhibited promising power conversion efficiencies of 4.84% and 4.70% with PC(61)BM (1?:?0.8 wt ratio) and PC(71)BM (1?:?0.6 wt ratio), respectively. 相似文献
993.
Posttranslational protein modification by small ubiquitin-related modifier (SUMO) has emerged as an important regulatory mechanism for chromosome segregation during mitosis. This review focuses on how SUMOylation regulates the centromere and kinetochore activities to achieve accurate chromosome segregation during mitosis. Kinetochores are assembled on the specialized chromatin domains called centromeres and serve as the sites for attaching spindle microtubule to segregate sister chromatids to daughter cells. Many proteins associated with mitotic centromeres and kinetochores have been recently found to be modified by SUMO. Although we are still at the early stage of elucidating how SUMOylation controls chromosome segregation during mitosis, a substantial progress has been achieved over the past decade. Furthermore, a major theme that has emerged from the recent studies of SUMOylation in mitosis is that both SUMO conjugation and deconjugation are critical for kinetochore assembly and disassembly. Lastly, we propose a model that SUMOylation coordinates multiple centromere and kinetochore activities to ensure accurate chromosome segregation. 相似文献
994.
A simple Schiff base type fluorescent receptor 1 was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an ‘off-on-type’ mode with high selectivity in the presence of Zn2+ ion. The selectivity of 1 for Zn2+ is the consequence of combined effects of chelation-enhanced fluorescence (CHEF), CN isomerization, and inhibition of photoinduced electron transfer (PET). 相似文献
995.
New concept on the promotion of immobilization and catalytic activity of enzyme on mesoporous silica through template micelles is proposed and realized in this paper. Proper P123 templates are controllable retained in the as-synthesized SBA-15, not only to anchor the horseradish peroxidase (HRP) guest, but also to establish the crowding-like microenvironment around the enzyme. The influence of retaining templates on the pore structure of SBA-15, immobilization, and catalytic activity of HRP is studied, and the possible process of template removal is proposed. Ethanol refluxing of 6 h is conformable to prepare the optimal mesoporous support characterized with the retained templates of about 8%. With the assistance of retained templates in SBA-15, up to 49 mg g(-1) of HRP can be immobilized, 100% more than that on calcined SBA-15. Furthermore, the thermal stability, the resistance of pH variation and denaturing agent urea, and the recycle usage of HRP immobilized are obviously elevated, paving a novel and low-cost route to develop enzyme catalysts. 相似文献
996.
Hong‐Xin Liu Jun‐Long Bi Yue‐Hu Wang Wei Gu Yao Su Fang Liu Shi‐Xian Yang Guang‐Wan Hu Ji‐Feng Luo Ge‐Fen Yin Chun‐Lin Long 《Helvetica chimica acta》2012,95(7):1231-1237
Methyl pothoscandensate ( 1 ), a new molecular skeleton of ent‐18(4→3)‐abeokaurane, along with eight known compounds was isolated from the whole plant of Pothos scandens. The structure of the new compound was established by spectroscopic techniques and confirmed by single‐crystal X‐ray diffraction. The inhibitory activity of selected compounds against porcine respiratory and reproductive syndrome virus (PRRSV) was measured by the cytopathic effect (CPE) method. Compound 1 showed weak effect on PRRSV with an IC50 value of 40.3±8.3 μM (TI=15.7). 相似文献
997.
Xue Bai Wan Qi Shi Hua Feng Chen Ping Zhang Ying Li Shu Fan Yin 《Chemistry of Natural Compounds》2012,48(1):60-65
New 4-chalcone ursolate and 1-acetyl-3-(4-phenyl)-4,5-dihydro-2-pyrazoline-5-phenyl ursolate derivatives were synthesized
by esterification of UA and chalcone or pyrazoline. The compounds were structurally confirmed by IR, 1H NMR, 13C NMR, and HR-MS spectroscopy. The cytotoxicity of ten derivatives was evaluated against A549, SKOV3, and HepG2 cell lines
by MTT assay. The result showed that several compounds were more potent than UA against A549 and SKOV3 cells; however, none
of them were more potent than UA against HepG2. 相似文献
998.
A series of novel bis-pyrazole/pyridine complexes, [Zn(2)(HL(1))(2)(μ(2)-SO(4))](2)·EtOH·H(2)O (1), [Co(2)(HL(1))(2)(μ(2)-SO(4))](2)·2DMF·6H(2)O (2), [Zn(4)(HL(1))(4)(μ(4)-SO(4))][OH](2) (3), [Zn(2)(HL(2))(2)(μ(2)-SO(4))]·2H(2)O (4), [Zn(H(2)L(2))(H(2)O)(2)](SO(4))·0.87H(2)O (5) (H(2)L(1) = 2,6-di-(5-phenyl-1H-pyrazol-3-yl)pyridine, H(2)L(2) = 2,6-di-(5-methyl-1H-pyrazol-3-yl)pyridine), were synthesized hydrothermally from the self-assembly of Zn(II) or Co(II) with different types of bipyrazolyl/pyridine derivative ligands. All the complexes were characterized by elemental analysis, IR and UV-vis spectroscopy, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction. Structural analyses revealed that metal atoms (Zn and Co) in complexes 1-5 are five-coordination modes, forming slightly distorted trigonal bipyramidal geometries. In complexes 1-3, H(2)L(1) ligand connected the two metal centers via the tetradentate fashion, and the same form of connection was found in complex 4 with H(2)L(2) ligand. While in complex 5, H(2)L(2) only connected with one metal center via the tridentate fashion, which was different from those in complexes 1-4. Additionally, there are abundant hydrogen bonding interactions in complexes 1-4. Interestingly, for hydrogen bonding connecting fashions being different, the molecules for the complexes 1 and 4 are held together by the hydrogen bond to form a 1D supramolecular structure, whereas complexes 2 and 3 are a hydrogen bonded dimer. In addition, quantum chemical calculations for 1, 3, and 4, thermal behaviors and photoluminescent properties for 1 and 3-5 were performed and discussed in detail. In the mean time, we found that these complexes had potential catalytic activity for the oxidation reaction of cyclohexane. 相似文献
999.
We investigate the electronic transport properties for a molecular device model constructed by a phenylene ethynylene oligomer molecular with different side groups embedding in a carbon chain between two graphene electrodes. Using the first-principles method, the unusual dual conductance, negative differential resistance (NDR) behavior with large peak to valley ratio, and obvious rectifying performance are numerically observed in such proposed molecular device. The analysis of the molecular projected self-consistent Hamiltonian and the evolution of the frontier molecular orbitals (MOs) as well as transmission coefficients under various external voltage biases gives an inside view of the observed results, which suggests that the dual conductance behavior and rectifying performance are due to the asymmetry distribution of the frontier MOs as well as the corresponding coupling between the molecule and electrodes. But the NDR behavior comes from the conduction orbital being suppressed at certain bias. Interestingly, the conduction properties can be tuned by introducing side groups to the molecule and the rectification as well as the NDR behavior (peak to valley ratio) can be improved by adding different side groups in the device model. 相似文献
1000.
An efficient rhodium/olefin-sulfoxide catalyzed asymmetric conjugate addition of organoboronic acids to a variety of nitroalkenes has been developed, where 2-methoxy-1-naphthyl sulfinyl functionalized olefin ligands have shown to be highly effective and are applicable to a broad scope of aryl, alkyl, and heteroaryl nitroalkenes. 相似文献