全文获取类型
收费全文 | 1261篇 |
免费 | 34篇 |
国内免费 | 13篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 20篇 |
2011年 | 28篇 |
2010年 | 18篇 |
2009年 | 29篇 |
2008年 | 33篇 |
2007年 | 30篇 |
2006年 | 29篇 |
2005年 | 51篇 |
2004年 | 66篇 |
2003年 | 67篇 |
2002年 | 43篇 |
2001年 | 45篇 |
2000年 | 36篇 |
1999年 | 49篇 |
1998年 | 42篇 |
1997年 | 43篇 |
1996年 | 59篇 |
1995年 | 55篇 |
1994年 | 59篇 |
1993年 | 47篇 |
1992年 | 55篇 |
1991年 | 44篇 |
1990年 | 22篇 |
1989年 | 39篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 2篇 |
排序方式: 共有1308条查询结果,搜索用时 15 毫秒
991.
Els Mannekens Dirk Tourwé Sylvia Vanderstichele Trang Nguyen Thi Diem Géza Tóth Antal Péter Nga N. Chung Peter W. Schiller 《Letters in Peptide Science》1995,2(3-4):190-192
Summary In order to influence side-chain conformations and to increase the -agonist properties of the -selective opioid receptor -antagonist H-Tyr-Tic-Phe-Phe-NH2, residues Tyr1, Phe3 and Phe4 were replaced by their -methyl-substituted stereoisomers. Synthesis of -Me-Tyr was carried out in a stereoselective way. Incorporation of the modified amino acids was performed by SPPS. Receptor binding data and GPI and MVD bioassays were obtained for all stereoisomers, in general showing equal or slightly increased potencies. In the [(R,S)-Me-Phe3]analogue, the introduction of the -methyl substituent restores signal transduction. 相似文献
992.
Jakob Weber 《Development genes and evolution》1995,205(3-4):171-181
The late stages of stenotele development and the migration and installation of freshly matured stenoteles in Hydra have been studied by kinetic and immunofluorescence investigations with rhodamine-labelled polyps. It was found that the high concentration of osmotic pressure-generating poly(-glutamic acid)s is synthesised exclusively within the lumen of the immature nematocyst. Assembly of the polymers, which is completed after approximately 0.5 days, is accompanied by a swelling of the capsule and ends when the cyst is mature. Active migration of the stenoteles to the tentacles begins only about 1.0 day later, and the time required for installation of a stenotele on the outer surface of the tissue amounts to about another 1.5 days. Furthermore, the results obtained suggest that the disintegration of the clusters of growing stenoteles, which begins 0.5 to 1.0 days before maturation, is a passive process; the ability of a nematocyte to migrate actively to the tentacles is acquired after maturation and might be controlled directly by regulating factors contained in the tissue.Abbreviations BrdU
5-bromo-2-deoxy-uridine
- BSA
bovine serum albumine
- DIC
differential-interference contrast
- DTE
1,4-dithioerythritol
- FITC
fluoresceinisothiocyanate
- MBS
m-maleimidobenzoyl-n-hydroxysuccinimide ester
- PBS
phosphate-buffered saline
- PEG
poly(ethylene glycol)
- p/GA
poly(a/y-glutamic acid)
- TRITC
tetramethyl-rhodamine6-isothiocyanate
- TROMI
tetramethyl-rhodamine-5/6-maleimide 相似文献
993.
1. The number and distribution pattern of -adrenergic receptors in the brain have been reported to be species specific. The aim of the present study was to describe binding of the -adrenoceptor ligand [125I]iodocyanopindolol in the brain of the tree shrew (Tupaia belangeri), a species which provides an appropriate model for studies of psychosocial stress and its consequences on central nervous processes.2. 125I-Iodocyanopindolol (125ICYP) labeling revealed a high degree of nonspecific binding, which was due mainly to interactions of this ligand with serotonin binding sites. For a quantitative evaluation of 1- and 2-adrenoceptors, serotonin binding sites had to be blocked by 100 M 5HT.3. Binding of the radioligand to 1- and 2-adrenoceptors was characterized using the 1-specific antagonist CGP20712A and the 2-specific antagonist ICI118.551. 1-adrenoceptor binding is present in the whole brain, revealing low receptor numbers in most brain regions (up to 1.5 to 2.7 fmol/mg). A slight enrichment was observed in cortical areas (lateral orbital cortex: 4.0±0.7 fmol/mg) and in the cerebellar molecular layer (8.7±1.0 fmol/mg).4. Competition experiments demonstrated high- and low-affinity binding sites with considerable variations in K
i values for CGP20712A, showing that various affinity states of 1-adrenoceptors are present in the brain (K
i: 0.61 nM to 67.1 M). In the hippocampus, only low-affinity 1-adrenoceptors were detected (K
i: 1.3±0.2 M). Since it is known that 125ICYP labels not only membrane bound but also internalized -adrenoceptors, it can be assumed that the large population of the low-affinity sites represents internalized receptors which may be abundant due to a high sequestration rate.5. High numbers of 2-adrenoceptors are present in only a few brain structures of tree shrews (external layer of the olfactory bulb, 15.8±2.0 fmol/mg; claustrum, 19.3±1.5 fmol/mg; anteroventral thalamic nucleus, 19.4±1.5 fmol/mg; cerebellar molecular layer, 55.0±4.3 fmol/mg). Also for this class of -adrenoceptors, high- and low-affinity binding sites for the 2-selective antagonist ICI118.551 were observed, indicating that 125ICYP labels membrane bound and internalized 2-adrenoceptors. Only in the cerebellar molecular layer was a high percentage of high-affinity 2-adrenoceptors detected (K
i for ICI118.551 was 1.8±0.3 nM for 90% of the receptors).6. In conclusion, 1- and 2-adrenoceptor binding can be localized and quantified by in vitro receptor autoradiography in the brains of tree shrews when serotonergic binding sites are blocked. Modulatory effects of long-term psychosocial conflict on the central nervous -adrenoceptor system in male tree shrews are described in the following paper. 相似文献
994.
Risto Renkonen Pirkko Mattila Marja-Leena Majuri Jarkko Rabina Sanna Toppila Jutta Renkonen Laura Hirvas Jaana Niittymaki Juha Pekka Turunen Ossi Renkonen Timo Paavonen 《Glycoconjugate journal》1997,14(5):593-600
Extravasation from the blood of malignant tumour cells that form metastasis and leukocytes that go into tissues require contact
between selectins and their sialyl Lewis x and sialyl Lewis a (sLex and sLea respectively) decorated ligands. Endothelial
cells have been shown to express sLex epitopes in lymph nodes and at sites of inflammation, and this is crucial for the selectin-dependent
leukocyte traffic. Besides the ability to synthesize sLex on sialylated N-acetyllactosamine via the action of α(1,3)fucosyltransferase(s),
endothelial cells can also degrade sLex to Lewis x through the action of α(2,3)sialidase(s). In addition, several epithelial
tumors possess the machinery to synthesize sLex, which facilitates their adhesion to endothelial E- and P-selectin.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
995.
Summary Continuous treatment of developing eggs of the polychete Ophryotrocha labronica with -methylornithine, which inhibits synthesis of putrescine, led to arrest of development at gastrulation. The present ultrastructural analysis suggests that the arrest of development is due to failure to form nuclei, and thus reveals a possible role for putrescine in nucleolar formation. Further support for this contention was provided by means of electron-microscopical autoradiography. It was found that newly synthesized putrescine, derived from administered 3H-ornithine, labeled the nucleoli intensely at the time of their normal appearance during gastrulation, the time at which the rate of endogenous putrescine synthesis is maximal. These observations have led to the conclusion that putrescine synthesis may be directly involved in formation of nucleoli.We thank Mrs Lena Olsson and Mrs Annagreta Petersen for excellent technical assistance. This investigation was supported by the Swedish Natural Science Research Council 相似文献
996.
Francis A. Williamson Prof. D. James Morré J. Shen-Miller 《Cell and tissue research》1976,170(4):477-484
Summary 5-Nucleotidase activity of rat liver plasma membrane is markedly inhibited by concanavalin A. Taken together with a unilateral pattern of labelling of concanavalin A binding sites with hemocyanin, the results indicate that an allosteric site of the enzyme is at the outer surface of the membrane.Work supported in part by NIH CA 13145 to D.J. Morré and by U.S. NASA W-12792(05) to J. Shen-Miller. Argonne National Laboratory is operated under the auspices of the U.S. Energy Research and Development Administration. We thank Keri Safranski, Dorothy Werderitish, and G.T. Chubb for technical assistance 相似文献
997.
Kylie Owen Rebecca A. Dunlop Jason P. Monty Daniel Chung Michael J. Noad David Donnelly Anne W. Goldizen Thomas Mackenzie 《Marine Mammal Science》2016,32(1):327-348
The movement of marine animals feeding at the sea surface is restricted by wave drag and a reduction in propulsive efficiency. Many rorqual whale species lunge feed at the surface, yet existing methodologies for detecting lunges in accelerometer data have not been applied to surface‐feeding behavior. Our study aimed to develop a method to detect surface‐feeding behavior in accelerometer data and in doing so, determine whether wave drag influences the detection of surface‐feeding behavior. A new acceleration parameter is described that considers the forward acceleration of the animal relative to its pitch. The new parameter, along with information on the deceleration and pitch angle, was then used in an automatic lunge detecting algorithm followed by a visual classification method that detected approximately 70% of the lunges observed during focal follow sampling. The forward acceleration of lunges decreased significantly with increasing proximity to the surface. This lower acceleration at the surface may influence the ability to detect lunge feeding behavior close to the surface. Future research should attempt to determine the cause of this relationship, which may be the influence of changes in the forces acting on the whale or behavioral flexibility by the whale. 相似文献
998.
Acylation of methyl--d-fructofuranoside and caprylic acid with an immobilized lipase, Novozym 435, was carried out in supercritical carbon dioxide (SCCO2) with tert-butanol as a co-solvent. Initial rate of acylation was 12-fold higher in SCCO2 than in tert-butanol. The equilibrium conversion was increased up to 70% with an increase in the molar ratio up to a maximum of 1:20 (methyl--d-fructofuranoside:caprylic acid) at 16 MPa and 70 °C. 相似文献
999.
Damien Lamotte Lorraine Buckberry Lucia Monaco Marco Soria Nigel Jenkins Jean-Marc Engasser Annie Marc 《Cytotechnology》1999,29(1):55-64
A non-human like glycosylation pattern in human recombinant glycoproteins expressed by animal cells may compromise their use as therapeutic drugs. In order to correct the CHO glycosylation machinery, a CHO cell line producing recombinant human interferon- (IFN) was transformed to replace the endogenous pseudogene with a functional copy of the enzyme 2,6-sialyltransferase (2,6-ST). Both the parental and the modified CHO cell line were propagated in serum-free batch culture with or without 1 mM sodium butyrate. Although Na-butyrate inhibited cell growth, IFN concentration was increased twofold. The IFN sialylation status was determined using linkage specific sialidases and HPLC. Under non- induced conditions, IFN expressed by 2,6-engineered cells contained 68% of the total sialic acids in the 2,6- conformation and the overall molar ratio of sialic acids to IFN was 2.3. Sodium butyrate addition increased twofold the molar ratio of total sialic acids to IFN and 82% of total sialic acids on IFN were in the 2,6-conformation. In contrast, no effect of the sodium butyrate was noticed on the sialylation of the IFN secreted by the 2,6-ST deficient parental cell line. This study deals for the first time with the effect of Na-butyrate on CHO cells engineered to produce human like sialylation. 相似文献
1000.
The use of a dissolvable solid matrix, -carrageenan, to quantify biomass grown on solid media was studied. A firm gel was obtained with 2% (w/v) -carrageenan and 20 mM K+ which could be easily dissolved in demineralized water. Direct quantification of Coniothyrium minitans biomass grown on this medium was feasible. No effects of the dissolution on the amount of biomass recovered were detected. 相似文献