全文获取类型
收费全文 | 19635篇 |
免费 | 1883篇 |
国内免费 | 641篇 |
专业分类
22159篇 |
出版年
2023年 | 132篇 |
2022年 | 315篇 |
2021年 | 472篇 |
2020年 | 321篇 |
2019年 | 413篇 |
2018年 | 472篇 |
2017年 | 350篇 |
2016年 | 592篇 |
2015年 | 965篇 |
2014年 | 1057篇 |
2013年 | 1253篇 |
2012年 | 1452篇 |
2011年 | 1429篇 |
2010年 | 938篇 |
2009年 | 739篇 |
2008年 | 1009篇 |
2007年 | 944篇 |
2006年 | 891篇 |
2005年 | 819篇 |
2004年 | 750篇 |
2003年 | 716篇 |
2002年 | 642篇 |
2001年 | 551篇 |
2000年 | 484篇 |
1999年 | 450篇 |
1998年 | 217篇 |
1997年 | 203篇 |
1996年 | 186篇 |
1995年 | 167篇 |
1994年 | 151篇 |
1993年 | 121篇 |
1992年 | 245篇 |
1991年 | 244篇 |
1990年 | 203篇 |
1989年 | 216篇 |
1988年 | 189篇 |
1987年 | 152篇 |
1986年 | 144篇 |
1985年 | 168篇 |
1984年 | 123篇 |
1983年 | 98篇 |
1982年 | 90篇 |
1981年 | 97篇 |
1979年 | 109篇 |
1978年 | 91篇 |
1977年 | 71篇 |
1976年 | 68篇 |
1975年 | 88篇 |
1974年 | 89篇 |
1973年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
A full-length zebrafish cDNA clone and a partial mouse cDNA clone similar to chick DM-GRASPwere isolated and analyzed. The nucleotide sequence of the full-length zebrafish clone shares 54% identity, and predicts 39% amino acid identity, with chick DM-GRASP. The partial mouse clone shares 76% nucleotide identity, and predicts 76% amino acid identity, with chick DM-GRASP. The predicted proteins encoded by both of these clones exhibit conserved structural domains that are characteristic of the chick protein. These features may identify them as a distinct subfamily within the immunoglobulin superfamily of cell adhesion molecules. Express of the zebrafish DM-GRASP protein is similar to chick DM-GRASP and is principally restricted to a small subset of developing sensory and motor neurons during axonogenesis. Zebrafish DM-GRASP expression was temporally regulated and limited to specific axon domains. This regional expression correlated with fasciculated axon domains. These results suggest that the zebrafish and mouse cDNA clones represent the respective fish and mammalian homologs of thick DM-GRASP. The highly selective expression of zebrafish DM-GRASP suggests that it is involved in the selective fasciculation and guidance of axons along their normal pathways. 1994 John Wiley & Sons, Inc. 相似文献
212.
213.
我们采用三硝基甲苯(TNT)与大鼠晶状体体外培养的方法,动态观察了晶状体中可溶性蛋白质、非蛋白质巯基、蛋白质巯基、蛋白质结合巯基及二硫键含量的变化,发现随着三硝基甲苯作用时间的延长,可溶性蛋白质、非蛋白质巯基及蛋白质巯基均减少,蛋白质结合巯基及二硫键交联的蛋白质含量增加,其中可溶性蛋白质、非蛋白质巯基及二硫键含量的变化皆达到了统计学上显著意义水平(P<0.05)。 相似文献
214.
本文利用SDS-聚丙烯酰胺凝胶电泳方法,定量研究了体外培养的软骨细胞和软骨组织基质中Ⅱ型胶原蛋白的含量。结果表明氧自由基(·O-2和·OH)和具有自由基性质的物质(黄腐酸,镰刀菌毒素)可使软骨细胞合成,分泌异常的非Ⅱ型的胶原蛋白,同时,硒化合物可明显地抑制此种效应。 相似文献
215.
The present study disclosed the cross-reactivity between Bermuda grass pollen (BGP) and other grass pollens using monoclonal antibodies (MAbs) and polyclonal antiserum. MAb 9–13, directed against a group of minor allergens of BGP (Cyn d Bd68K, 48K, 38K) was found to cross-react with extracts of ten other grass pollens. Immunoblotting assays illustrated that MAb 9–13 cross-reacted with multiple components of most of these pollens, and the major cross-reactive components had molecular weights of 29–36 kD. The cross-reactivity between BGP andLol pI, the group I allergen of rye grass pollen, was further evaluated;Lol pI was recognized by MAb 9–13, but not by our MAbs/polyclonal antiserum againstCyn dI, the major allergen of BGP. These results suggest that the epitope recognized by MAb 9–13 is a common (C) epitope shared byLol pI andCyn d Bd68K, 48K, 38K, andCyn dI does not share significant antigenicity withLol pI. In a modified radio-allergosorbent test, IgE antibodies in the serum of BGP-allergic patients reacted mildly with C-epitope-bearing components of both BGP and rye grass pollens, and this binding could be blocked specifically by MAb 9–13. This suggests that in addition to an antigenic cross-reaction, the C epitope can also lead to an allergenic cross-reaction. 相似文献
216.
L.-Y. Chau T. A. Lin W.-T. Chang C.-H. Chen M.-J. Shue Y.-S. Hsu C.-Y. Hu W.-H. Tsai G. Y. Sun 《Journal of neurochemistry》1993,60(2):454-460
Abstract: Addition of endothelins (ETs) to neuroblastomaglioma hybrid cells (NG108-15) induced increases in cytosolic free Ca2+ ([Ca2+]i) levels of labeled inositol monophosphates and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. The increases in [Ca2+]i elicited by the three ETs (ET-1, ET-2, and ET-3) were transient and did not show a sustained phase. Chelating extracellular Ca2+ in the medium by adding excess EGTA decreased the ET-mediated Ca2+ response by 40-50%. This result indicates that a substantial portion of the increase in [Ca2+]i was due to influx from an extracellular source. However, the increase in [Ca2+]i was not affected by verapamil or nifedipine (10?5M). A rank order potency of ET-1 ET-2 ET-3 is shown for the stimulated increase in [Ca2+]i, as well as labeled inositol phosphates, in these cells. ATP (10?4M) and bradykinin (10?7M) also induced the increases in [Ca2+]i and Ins(1,4,5)P3 in NG108-15 cells, albeit to a different extent. When compared at 10?7M, bradykinin elicited a five- to sixfold higher increase in the level of Ins(1,4,5)P3, but less than a twofold higher increase in [Ca2+]i than those induced by ET-1. Additive increases in both Ins(1,4,5)P3 and [Ca2+]i were observed when ET-1, ATP, and bradykinin were added to the cells in different combinations, suggesting that each receptor agonist is responsible for the hydrolysis of a pool of polyphosphoinositide within the membrane. ET-1 exhibited homologous desensitization of the Ca2+ response, but partial heterologous desensitization to the Ca2+ response elicited by ATP. On the contrary, ET-1 did not desensitize the response elicited by bradykinin, although bradykinin exhibited complete heterologous desensitization to the response elicited by ET-1. Taken together, these results illustrate that, in NG108-15 cells, a considerable amount of receptor cross talk occurs between ET and other receptors that transmit signals through the polyphosphoinositide pathway. 相似文献
217.
The essential mitotic target of calmodulin is the 110-kilodalton component of the spindle pole body in Saccharomyces cerevisiae. 总被引:17,自引:0,他引:17 下载免费PDF全文
J R Geiser H A Sundberg B H Chang E G Muller T N Davis 《Molecular and cellular biology》1993,13(12):7913-7924
Two independent methods identified the spindle pole body component Nuf1p/Spc110p as the essential mitotic target of calmodulin. Extragenic suppressors of cmd1-1 were isolated and found to define three loci, XCM1, XCM2, and XCM3 (extragenic suppressor of cmd1-1). The gene encoding a dominant suppressor allele of XCM1 was cloned. On the basis of DNA sequence analysis, genetic cosegregation, and mutational analysis, XCM1 was identified as NUF1/SPC110. Independently, a C-terminal portion of Nuf1p/Spc110p, amino acid residues 828 to 944, was isolated as a calmodulin-binding protein by the two-hybrid system. As assayed by the two-hybrid system, Nuf1p/Spc110p interacts with wild-type calmodulin and triple-mutant calmodulins defective in binding Ca2+ but not with two mutant calmodulins that confer a temperature-sensitive phenotype. Deletion analysis by the two-hybrid system mapped the calmodulin-binding site of Nuf1p/Spc110p to amino acid residues 900 to 927. Direct binding between calmodulin and Nuf1p/Spc110p was demonstrated by a modified gel overlay assay. Furthermore, indirect immunofluorescence with fixation procedures known to aid visualization of spindle pole body components localized calmodulin to the spindle pole body. Sequence analysis of five suppressor alleles of NUF1/SPC110 indicated that suppression of cmd1-1 occurs by C-terminal truncation of Nuf1p/Spc110p at amino acid residues 856, 863, or 881, thereby removing the calmodulin-binding site. 相似文献
218.
Huili Feng Jiahuan Guo Changhui Peng Daniel Kneeshaw Gabrielle Roberge Chang Pan Xuehong Ma Dan Zhou Weifeng Wang 《Global Change Biology》2023,29(14):3970-3989
A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m−2 year−1) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%–32.1%) and 14.7% (11.6%–17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition. 相似文献
219.
Dr. B. W. Kim Mr. E. H. Kim Mr. S. C. Lee Professor H. N. Chang 《Bioprocess and biosystems engineering》1993,8(5-6):263-269
Traditional application of computer to fermentation processes has focused on the measurement and control of parameters such as temperature, pH, vessel pressure, sparge rate, dissolved oxygen, substrate concentration, and product concentration. In a fed-batch reactor with the photosynthetic green sulfur bacterium Chlorobium thiosulfatophilum which converts hydrogen sulfide to elementary sulfur or sulfate, separate measurement of cell mass concentration and sulfur particle concentration turbidimetrically was difficult due to their combined contributions to the total turbidity. Instead of on-line measurement of many process variables, a model-based control of feed rate and illuminance was designed. Optimal operation condition relating feed rate vs. light intensity was obtained to suppress the accumulation of sulfate and sulfide, and to save light energy in a 4-1 photosynthetic fed-batch reactor. This relation was correlated with the inreasing cell mass concentration. A model which describes the cell growth by considering the light attenuation effects due to scattering and absorption, and to crowding effect of the cells, was established beforehand with the results from the experiments. Based on these optimal operating conditions and the cell growth model, automatic controls of feed rate and illuminance were carried out alternatively to the traditional application of computer to fermentation with on-line measurement, realtime response and adjustment of process variables.List of Symbols
F ml/min
Flow rate of gas mixture
-
hV lux
Average illuminance
-
Q mmol/(l h)
Removal rate of hydrogen sulfide
-
X mg protein/l
Cell mass concentration as protein
-
X
0 mg protein/l
Initial cell mass concentration
-
X
m mg protein/l
Maximum cell mass concentration
-
a h–1
Apparent specific growth rate 相似文献
220.
Fu-Chou Cheng Jon-Son Kuo Wen-Ho Chang Dong-Juiing Juang Ying Shih Jeng-Shiow Lai 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1993,617(2)
The simultaneous measurement of homovanillic acid, 3,4-dihydroxyphenylacetic acid, serotonin and 5-hydroxyindoleacetic acid in human plasma by an ultrafiltration and microbore high-performance liquid chromatography—electrochemical detection technique is established. Conventional preparation of blood is very tedious and time-consuming, but isocratic separation of the analytes in plasma ultrafiltrates using a microbore column could be achieved within 10 min. Hence, theoretically, over 140 analyses can be performed in a working day. The detection limit (signal-to-noise ratio = 3) of this method is about 0.1–0.5 pg per injection for all analytes. The required volume of plasma samples can be less than 100 μl. Hence, blood loss is minimal, especially in repeated blood sampling. This rapid, simple and sensitive method can, therefore, be used as a routine clinical tool in the simultaneous measurement of plasma homovanillic acid, 3,4-dihydroxyphenylacetic acid, serotonin and 5-hydroxyindoleacetic acid. 相似文献