全文获取类型
收费全文 | 1378篇 |
免费 | 58篇 |
国内免费 | 21篇 |
专业分类
化学 | 801篇 |
晶体学 | 9篇 |
力学 | 60篇 |
数学 | 264篇 |
物理学 | 323篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 9篇 |
2020年 | 29篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 25篇 |
2014年 | 49篇 |
2013年 | 68篇 |
2012年 | 96篇 |
2011年 | 84篇 |
2010年 | 65篇 |
2009年 | 57篇 |
2008年 | 76篇 |
2007年 | 75篇 |
2006年 | 85篇 |
2005年 | 63篇 |
2004年 | 57篇 |
2003年 | 56篇 |
2002年 | 41篇 |
2001年 | 35篇 |
2000年 | 33篇 |
1999年 | 14篇 |
1998年 | 19篇 |
1997年 | 12篇 |
1996年 | 16篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 9篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 20篇 |
1975年 | 14篇 |
1973年 | 5篇 |
排序方式: 共有1457条查询结果,搜索用时 15 毫秒
51.
Kin-Ho Law Pui-Ling Chan Wai-Sum Lau Yin-Chung Cheng Yun-Chung Leung Wai-Hung Lo Hugh Lawford Hoi-Fu Yu 《Applied biochemistry and biotechnology》2004,114(1-3):361-372
Plastic wastes constitute a worldwide environmental problem, and the demand for biodegradable plastics has become high. One
of the most important characteristics of microbial polyesters is that they are thermoplastic with environmentally degradable
properties. In this study, pUC 19/PHA was cloned and transformed into three different Escherichia coli strains. Among the three strains that were successfully expressed in the production of polyhydroxyalkanoates (PHA), E. coli HMS174 had the highest yield in the production of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[HB-HV]). The cell dry
weight and PHA content of recombinant HMS174 reached as high as 10.27 g/L and 43% (w/w), respectively, in fed-batch fermentor
culture. The copolymer of PHA, P(HB-HV), was found in the cells, and the biopolymers accumulated were identified and analyzed
by gas chromatography, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. We demonstrated
clearly that the E. coli host for PHA production has to be carefully selected to obtain a high yield. The results obtained indicated that a superior
E. coli with high PHA production can be constructed with a desirable ratio of P(HB-HV), which has potential applications in industry
and medicine. 相似文献
52.
A custom-built multi-technique portable spectrometer was used to study the vibrational (and electronic) excitations associated with the “anomalous” CO adsorption recently observed on clean and oxidized Cu(100) surfaces at room temperature. Results from the electron energy loss (and thermal desorption) experiments have provided strong evidence for in-situ CO production induced by low-energy electron or ion irradiation of CO or C2H4 on Cu(100). In particular, the C-O vibrational stretch frequency for the room-temperature CO adsorption was found to be red-shifted by 9 meV from its nominal position (259 meV) and could be observed even at temperature as high as 420 K. Several plausible mechanisms involving coadsorbate interactions with CO on metal surfaces have been discussed. A direct interaction model involving partial bonding between CO, adsorbed on an atop site, and a coadsorbed O atom in a four-fold hollow site was found to be adequate in explaining the observed red shift and the apparent stabilization of CO on Cu(100) at room temperature. 相似文献
53.
Fiedler D Leung DH Bergman RG Raymond KN 《Journal of the American Chemical Society》2004,126(12):3674-3675
A supramolecular metal-ligand assembly encapsulates a variety of cationic half-sandwich ruthenium complexes. Due to the chirality of both host and guest, chiral recognition is observed with diastereomeric excesses up to 70%. The chiral cavity can be used to carry out a dynamic resolution of the rapidly equilibrating enantiomers of the chiral organometallic guest. 相似文献
54.
55.
56.
57.
Mishra SR Leung WC Arroyo C Bachmann KT Blair RE Foudas C King BJ Lefmann WC Oltman E Quintas PZ Rabinowitz SA Sciulli FJ Seligman WG Shaevitz MH Merritt FS Oreglia MJ Schumm BA Bernstein RH Borcherding F Fisk HE Lamm MJ Marsh W Merritt KW Schellman H Yovanovitch DD Bodek A Budd HS de Barbaro P Sakumoto WK Sandler PH Smith WH 《Physical review letters》1992,69(24):3499-3502
58.
[reactions: see text] [(Ph3P)CuH]6 effectively catalyzes the hydrostannation of activated alkynes with exclusive regioselectivity for alpha-stannation. Syn hydrostannation is observed exclusively for alkynoates. Anti or syn hydrostannation adducts are obtained as products for alkynone substrates. 相似文献
59.
Pyropheophorbide-a methyl ester (MPPa) is a semisynthetic photosensitizer derived from chlorophyll a. The absorption peak of MPPa in organic solvent and in cells was at 667 and 674 nm, respectively. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay showed that MPPa had no dark cytotoxicity. In vitro photodynamic activity was extensively evaluated using a human lung carcinoma cancer cell line (NCI-h446). MPPa exhibited no genotoxicity, as assayed by single-cell gel electrophoresis. Using confocal laser scanning microscopy and organelle-specific fluorescent probes, MPPa was found to localize in the intracellular membrane system, namely the endoplasmic reticulum, Golgi apparatus, lysosomes and mitochondria, in the NCI-h446 cells. Furthermore, nuclear staining and DNA gel electrophoresis revealed that DNA condensation and fragmentation occurred post-photodynamic therapy, indicating the cell death was in the apoptotic mode. 相似文献
60.
Leung PS 《Current protein & peptide science》2004,5(4):267-273
The peptide hormone angiotensin II is well established to play an endocrine role in the regulation of blood pressure, fluid and electrolyte homeostasis. In addition to its hemodynamic function, recent studies have shown that numerous tissues and organs contain their own locally generated angiotensin products (angiotensin II, III, IV and Ang 1-7) and they exhibit their respective activities. Such an intrinsic angiotensin-generating system renders to specific tissue function of our body, frequently via the regulatory mechanism of a paracrine, autocrine or intracrine manner. These tissues and organs include, to name but a few, the brain, bone marrow, adipose, epididymis, carotid body, liver, and pancreas. This local system has been shown to be responsive to various stimuli of physiological and pathophysiological importance. Moreover, the locally generated angiotensin peptides have multiple and novel actions including cell growth, anti-proliferation, apoptosis, reactive oxygen species generation, hormonal secretion, pro-inflammatory, and pro-fibrogenic actions, as well as vasoconstriction and vasodilatation. Notwithstanding the emerging roles of angiotensin II in various tissues and organs, the physiological significance and ultimately the clinical relevance remain largely undefined. Future target for these new functions by making use of specific renin-angiotensin system inhibitors, such as the angiotensin-converting enzyme and angiotensin II receptor blockers either in mono-therapy or in combination, could be of clinical importance. The current review is to focus on some of the new functions arising from the locally formed angiotensin II in tissues and organs, with particular attention to its emerging roles in the liver and the pancreas. 相似文献