全文获取类型
收费全文 | 32671篇 |
免费 | 2549篇 |
国内免费 | 1387篇 |
专业分类
36607篇 |
出版年
2024年 | 73篇 |
2023年 | 274篇 |
2022年 | 703篇 |
2021年 | 1058篇 |
2020年 | 748篇 |
2019年 | 952篇 |
2018年 | 1082篇 |
2017年 | 837篇 |
2016年 | 1285篇 |
2015年 | 1915篇 |
2014年 | 2255篇 |
2013年 | 2408篇 |
2012年 | 2965篇 |
2011年 | 2838篇 |
2010年 | 1710篇 |
2009年 | 1541篇 |
2008年 | 1967篇 |
2007年 | 1756篇 |
2006年 | 1585篇 |
2005年 | 1391篇 |
2004年 | 1371篇 |
2003年 | 1098篇 |
2002年 | 898篇 |
2001年 | 702篇 |
2000年 | 609篇 |
1999年 | 475篇 |
1998年 | 278篇 |
1997年 | 228篇 |
1996年 | 196篇 |
1995年 | 165篇 |
1994年 | 147篇 |
1993年 | 92篇 |
1992年 | 171篇 |
1991年 | 124篇 |
1990年 | 124篇 |
1989年 | 112篇 |
1988年 | 71篇 |
1987年 | 73篇 |
1986年 | 48篇 |
1985年 | 50篇 |
1984年 | 46篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1975年 | 14篇 |
1974年 | 11篇 |
1966年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
Lan Phi NT Nishiyama C Choi HS Sawamura M 《Bioscience, biotechnology, and biochemistry》2006,70(8):1832-1838
The characteristic aroma compounds of Citrus natsudaidai Hayata essential oil were evaluated by a combination of instrumental and sensory methods. Sixty compounds were identified and quantified, accounting for 94.08% of the total peel oil constituents. Limonene was the most abundant compound (80.68%), followed by gamma-terpinene (5.30%), myrcene (2.25%) and alpha-pinene (1.30%). Nineteen compounds which could not be identified in the original oil were identified in the oxygenated fraction. Myrcene, linalool, alpha-pinene, beta-pinene, limonene, nonanal, gamma-terpinene, germacrene D, and perillyl alcohol were the active aroma components (FD-factor > 3(6)), whereas beta-copaene, cis-sabinene hydrate and 1-octanol were suggested as characteristic aroma compounds, having a Natsudaidai-like aroma in the GC effluent. Three other compounds, heptyl acetate, (E)-limonene oxide and 2,3-butanediol, which each showed a high RFA value (>35) were considered to be important in the reconstruction of the original Natsudaidai oil from pure odor chemicals. The results indicate that 1-octanol was the aroma impact compound of C. natsudaidai Hayata peel oil. 相似文献
222.
We developed a new approach that employs a novel computer algorithm for the sensitive and high-throughput analysis of tertiary and quaternary interaction sites from chemically cross-linked proteins or multi-protein complexes. First, we directly analyze the digests of the chemically cross-linked proteins using only high-accuracy LC-MS/MS data. We analyze these data using a computer algorithm, we term X!Link, to find cross-links between two peptides. Our algorithm is rapid, taking only a few seconds to analyze approximately 5000 MS/MS spectra. We applied this algorithm to analyze cross-linked sites generated chemically using the amino specific reagent, BS3, in both cytochrome c and the mitochondrial division dynamin mutant, Dnm1G385D, which exists as a stable homodimer. From cytochrome c, a well-established test protein, we identified a total of 31 cross-links, 21 interpeptide and 10 intrapeptide cross-links, in 257 MS/MS spectra from a single LC-MS/MS data set. The high sensitivity of this technique is indicated by the fact that all 19 lysines in cytochrome c were detected as a cross-link product and 33% of all the Lys pairs within 20 A were also observed as a cross-link. Analysis of the cross-linked dimeric form of Dnm1G385D identified a total of 46 cross-links, 38 interpeptide and 8 intrapeptide cross-links, in 98 MS/MS spectra in a single LC-MS/MS data set. These results represent the most abundant cross-links identified in a single protein or protein dimer to date. Statistical analysis suggests a 1% false discovery rate after optimization of filtering parameters. Further analysis of the cross-links identified using our approach indicates that careful manual inspection is important for the correct assignment of cross-linking sites when multiple cross-linkable sites or several similar sequences exist. In summary, we have developed a sensitive MS-based approach to identify peptide-peptide cross-links that does not require isotopic labeling or comparison with non-cross-linked controls, making it faster and simpler than current methodologies. 相似文献
223.
224.
225.
Insulin contains two inter-chain disulfide bonds between the A and B chains (A7-B7 and A20-B19), and one intra-chain linkage in the A chain (A6-A11). To investigate the role of each disulfide bond in the structure, function and stability of the molecule, three des mutants of human insulin, each lacking one of the three disulfide bonds, were prepared by enzymatic conversion of refolded mini-proinsulins. Structural and biological studies of the three des mutants revealed that all three disulfide bonds are essential for the receptor binding activity of insulin, whereas the different disulfide bonds make different contributions to the overall structure of insulin. Deletion of the A20-B19 disulfide bond had the most substantial influence on the structure as indicated by loss of ordered secondary structure, increased susceptibility to proteolysis, and markedly reduced compactness. Deletion of the A6-A11 disulfide bond caused the least perturbation to the structure. In addition, different refolding efficiencies between the three des mutants suggest that the disulfide bonds are formed sequentially in the order A20-B19, A7-B7 and A6-A11 in the folding pathway of proinsulin. 相似文献
226.
目的:制备稳定、特异、高亲和性的分别针对甲型副伤寒沙门菌、乙型副伤寒沙门菌、丙型副伤寒沙门菌、肠炎沙门菌、伤寒沙门菌和猪霍乱沙门菌的单克隆抗体。方法:用甲醛灭活的菌液抗原免疫BALB/c小鼠,取脾细胞与SP2/0骨髓瘤细胞融合;用灭活的菌液包被酶标板,ELISA筛选阳性克隆株,建立细胞系;选取高效分泌杂交瘤细胞,常规制备腹水并纯化,进行单抗特异性与亲和性评价。结果:筛选得到分泌6种沙门菌相应单克隆抗体的杂交瘤细胞株,获得高亲和性单抗;所有单抗与大部分病原菌(包括7种沙门菌、3株志贺菌、2株李斯特菌、4株致病性大肠杆菌、2株霍乱弧菌)无交叉反应,但由于同类型O抗原的广泛分布,抗乙型副伤寒沙门菌单抗与鼠伤寒沙门菌、抗伤寒沙门菌单抗与肠炎沙门菌有明显的交叉反应。结论:沙门菌单抗的制备,为感染性腹泻的监测、诊断奠定了基础。 相似文献
227.
Qian Jia HongTao Wu XingJun Zhou Jian Gao Wei Zhao JouDi Aziz JingShuang Wei Lihua Hou Shuyin Wu Ying Zhang XiangFeng Dong YanMin Huang WeiYuan Jin HongJie Zhu XinHui Zhao ChunHua Huang LiPing Xing Liwen Li Jun Ma Xiyan Liu Ran Tao ShuaiDong Ye YiGao Song LingLing Song GuanPing Chen ChunLing Du XueTing Zhang Bo Li YanTao Wang Wei Yang Gilbert Rishton YuYang Teng GouQing Leng LuanFeng Li WenXian Liu LiJun Cheng QiuBo Liang ZhengWu Li XiuQin Zhang Yajun Zuo Wei Chen Huicheng Li Matthew Hui 《中国科学:生命科学英文版》2010,53(1):94-100
High mammalian gene expression was obtained for more than twenty different proteins in different cell types by just a few laboratory scale stable gene transfections for each protein. The stable expression vectors were constructed by inserting a naturally-occurring 1.006 kb or a synthetic 0.733 kb DNA fragment (including intron) of extremely GC-rich at the 5′ or/and 3′ flanking regions of these protein genes or their gene promoters. This experiment is the first experimental evidence showing that a non-coding extremely GC-rich DNA fragment is a super “chromatin opening element” and plays an important role in mammalian gene expression. This experiment has further indicated that chromatin-based regulation of mammalian gene expression is at least partially embedded in DNA primary structure, namely DNA GC-content. 相似文献
228.
229.
本文通过降低培养基中血清含量,向RPMI 1640培养基中补加三碘甲腺原氨酸而获得一种人胸腺网状上皮细胞占优势生长的培养物。在此培养基中细胞经传代培养长达90天,仍维持正常形态特征。胸腺组织在培养14天后,新生细胞的突起形成网状结构,细胞化学检查和电镜观察表明具有丰富的分泌颗粒,囊泡及张力原纤维束和桥粒等上皮细胞特征。收集合并细胞培养液,经部分纯化后检查其生物活性,表现出具有促进玫瑰花结形成和降低胸腺细胞TdT活性的作用,说明培养细胞的分泌产物具有胸腺激素活性。根据形态学,细胞化学和生物活性检测结果,我们倾向于认为该培养物主要为网状上皮细胞。 相似文献
230.
C. Ganesh Kumar Han-Seung Joo Jang-Won Choi Yoon-Moo Koo Chung-Soon Chang 《Enzyme and microbial technology》2004,34(7):673-681
During the course of investigation of haloalkalophilic bacteria, we screened some heavily polluted soil samples from the mudflats surrounding the city of Inchon, Korea, for their bioflocculant producing ability. Based on the screening, one isolate no. 450 tentatively identified as Bacillus sp. produced an extracellular polysaccharide having flocculation activity. The isolate produced the polysaccharide during the late logarithmic growth phase. The polymer could be recovered from the supernatant of the fermented medium by cold ethanol precipitation and purified by treating with cetylpyridinium chloride (CPC). The polymer was identified as an acidic polysaccharide containing neutral sugars, namely, galactose, fructose, glucose and raffinose, and uronic acids as major and minor components, respectively. The amount of neutral sugars, uronic acid and amino sugars were 52.4, 17.2 and 2.4%, respectively. The molecular weight of the polysaccharide was found to be 2.2×106 Da. The Fourier transform infrared spectrophotometer (FT-IR) revealed typical characteristics of polysaccharides. 1H NMR spectrum showed that the polymer is a heteroglycan. Thermogravimetric (TGA) analysis indicated the degradation temperature (Td) at 290 °C. The rheological analysis of the polymer 450 revealed the pseudoplastic property with shear-thinning effect, while the compression test indicated that the polymer had high gel strength, and the S.E.M. studies showed that the polymer has a porous structure with small pore-size distribution indicating the compactness of the polymer. 相似文献