全文获取类型
收费全文 | 2979篇 |
免费 | 284篇 |
专业分类
3263篇 |
出版年
2022年 | 11篇 |
2021年 | 38篇 |
2020年 | 28篇 |
2019年 | 18篇 |
2018年 | 36篇 |
2017年 | 26篇 |
2016年 | 59篇 |
2015年 | 92篇 |
2014年 | 106篇 |
2013年 | 132篇 |
2012年 | 173篇 |
2011年 | 195篇 |
2010年 | 141篇 |
2009年 | 128篇 |
2008年 | 195篇 |
2007年 | 189篇 |
2006年 | 203篇 |
2005年 | 152篇 |
2004年 | 169篇 |
2003年 | 165篇 |
2002年 | 166篇 |
2001年 | 39篇 |
2000年 | 36篇 |
1999年 | 40篇 |
1998年 | 42篇 |
1997年 | 51篇 |
1996年 | 42篇 |
1995年 | 46篇 |
1994年 | 31篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 28篇 |
1989年 | 34篇 |
1988年 | 35篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 23篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 24篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 15篇 |
1974年 | 8篇 |
1969年 | 9篇 |
排序方式: 共有3263条查询结果,搜索用时 0 毫秒
991.
Gunda Keilich Reinhard Brossmier Volker Eschenfelder Leif Holmquist 《Carbohydrate research》1975,40(2)
The circular dichroism spectra of a number of N-acetylneuraminic acid derivatives in aqueous solution were studied. For all compounds, the Cotton effects were found to be in the spectral range of the acetamido and carboxyl chromophores. The c.d. curves of the methyl, ethyl, and allyl α-
-ketosides are characterized by a broad, positive band centered at λ ≈ 195 nm with a slight skew towards the higher wavelengths and weak bands between λ 225 and 255 nm, whereas the methyl β-
-ketoside and the corresponding methyl ester show only an intense positive band with a broad shoulder in the same spectral range. 5-Acetamido-3,5-dideoxy-
-glycero-β-
-galacto-nonulopyranose, its methyl β-
-ketoside, and 5-acetamido-3,5-dideoxy-
-glycero-
-galacto-nonulopyranosonamide containing only the acetamido chromophore showed one single positive Cotton effect centered at λ ≈ 192 nm. The c.d. spectrum of 5-acetamido-3,5-dideoxy-
-glycero-
-galacto-nonulopyranosonic acid confirms the β-
configuration of the free acid in aqueous solution, whereas the shape of the c.d. curve of O-(N-acetyl-α-
-neuraminopyranosyl)-(2→3)-O-β-
-galactopyranosyl-(1→4)-
-glucopyranose resembles that of the methyl, ethyl, and allyl α-
-ketosides 2-4. 相似文献
992.
Reinhard Bolliger Hans Zürrer Reinhard Bachofen 《Applied microbiology and biotechnology》1985,23(2):147-151
Summary From enrichment cultures inoculated with water and sediments of a waste-water pond of a sugar refinery several photosynthetic nonsulphur bacteria have been isolated and tested for the ability to produce molecular hydrogen in the light. Strains have been found that utilize the freshly used, untreated waste substrate with higher yields than the laboratory strain used so far. Under the test conditions one strain showed higher hydrogen production rates from waste water than from any synthetic substrate. 相似文献
993.
994.
Reinhard F. M. Van Steveninck Margaret E. Van Steveninck André Läuchli 《Physiologia plantarum》1988,72(1):1-7
External application of abscisic acid (ABA) induces a relatively high rate of xylem exudation in excised roots of Lupinus luteus L. cv. Weiko III. The response is relatively slow with a lag period of ca 1 h. It is also slowly, but reversibly, abolished by application of 3.6 or 36 μ M cycloheximide (CHX). Contrary to expectation, K+ is not a significant factor in maintaining flow rates in lupin roots as no response was measured after adding K+ to root systems, from which K+ had been withheld for periods ranging from 3 h to several days. In fact, excised roots obtained from seedlings raised in the absence of K+ failed to respond to added K+ . Total depletion of K+ is difficult to achieve, because of initial seed reserves, and prolonged exudation in lupins can be maintained utilising only a small proportion of the K+ originally present in the root tissue. Nevertheless, the data cast doubt on the general applicability of the concept that volume flow is maintained by an osmotic gradient with K+ as the principal mineral ion. 相似文献
995.
996.
Zhonghua Wang Trevor Yeats Hong Han Reinhard Jetter 《The Journal of biological chemistry》2010,285(39):29703-29712
The first committed step in triterpenoid biosynthesis is the cyclization of oxidosqualene to polycyclic alcohols or ketones C30H50O. It is catalyzed by single oxidosqualene cyclase (OSC) enzymes that can carry out varying numbers of carbocation rearrangements and, thus, generate triterpenoids with diverse carbon skeletons. OSCs from diverse plant species have been cloned and characterized, the large majority of them catalyzing relatively few rearrangement steps. It was recently predicted that special OSCs must exist that can form friedelin, the pentacyclic triterpenoid whose formation involves the maximum possible number of rearrangement steps. The goal of the present study, therefore, was to clone a friedelin synthase from Kalanchoe daigremontiana, a plant species known to accumulate this triterpenoid in its leaf surface waxes. Five OSC cDNAs were isolated, encoding proteins with 761–779 amino acids and sharing between 57.4 and 94.3% nucleotide sequence identity. Heterologous expression in yeast and GC-MS analyses showed that one of the OSCs generated the steroid cycloartenol together with minor side products, whereas the other four enzymes produced mixtures of pentacyclic triterpenoids dominated by lupeol (93%), taraxerol (60%), glutinol (66%), and friedelin (71%), respectively. The cycloartenol synthase was found expressed in all leaf tissues, whereas the lupeol, taraxerol, glutinol, and friedelin synthases were expressed only in the epidermis layers lining the upper and lower surfaces of the leaf blade. It is concluded that the function of these enzymes is to form respective triterpenoid aglycones destined to coat the leaf exterior, probably as defense compounds against pathogens or herbivores. 相似文献
997.
998.
Kristin Kruse Christina Janko Vilma Urbonaviciute Claudia T. Mierke Thomas H. Winkler Reinhard E. Voll Georg Schett Luis E. Muñoz Martin Herrmann 《Apoptosis : an international journal on programmed cell death》2010,15(9):1098-1113
Systemic lupus erythematosus (SLE) is a complex disease resulting from inflammatory responses of the immune system against
several autoantigens. Inflammation is conditioned by the continuous presence of autoantibodies and leaked autoantigens, e.g.
from not properly cleared dying and dead cells. Various soluble molecules and biophysical properties of the surface of apoptotic
cells play significant roles in the appropriate recognition and further processing of dying and dead cells. We exemplarily
discuss how Milk fat globule epidermal growth factor 8 (MFG-E8), biophysical membrane alterations, High mobility group box 1
(HMGB1), C-reactive protein (CRP), and anti-nuclear autoantibodies may contribute to the etiopathogenesis of the disease.
Up to date knowledge about these key elements may provide new insights that lead to the development of new treatment strategies
of the disease. 相似文献
999.
Genome-wide microarrays have suggested that Emdogain regulates TGF-β target genes in gingival and palatal fibroblasts. However, definitive support for this contention and the extent to which TGF-β signaling contributes to the effects of Emdogain has remained elusive. We therefore studied the role of the TGF-β receptor I (TGF-βRI) kinase to mediate the effect of Emdogain on palatal fibroblasts. Palatal fibroblasts were exposed to Emdogain with and without the inhibitor for TGF-βRI kinase, SB431542. Emdogain caused 39 coding genes to be differentially expressed in palatal fibroblasts by microarray analysis (p<0.05; >10-fold). Importantly, in the presence of the TGF-βRI kinase inhibitor SB431542, Emdogain failed to cause any significant changes in gene expression. Consistent with this mechanism, three independent TGF-βRI kinase inhibitors and a TGF-β neutralizing antibody abrogated the increased expression of IL-11, a selected Emdogain target gene. The MAPK inhibitors SB203580 and U0126 lowered the impact of Emdogain on IL-11 expression. The data support that TGF-βRI kinase activity is necessary to mediate the effects of Emdogain on gene expression in vitro. 相似文献
1000.
André Fischer Nils Enkler Gerd Neudert Marco Bocola Reinhard Sterner Rainer Merkl 《BMC bioinformatics》2009,10(1):54