全文获取类型
收费全文 | 5304篇 |
免费 | 310篇 |
国内免费 | 2篇 |
专业分类
5616篇 |
出版年
2023年 | 19篇 |
2022年 | 38篇 |
2021年 | 89篇 |
2020年 | 56篇 |
2019年 | 75篇 |
2018年 | 96篇 |
2017年 | 88篇 |
2016年 | 135篇 |
2015年 | 183篇 |
2014年 | 210篇 |
2013年 | 365篇 |
2012年 | 353篇 |
2011年 | 364篇 |
2010年 | 230篇 |
2009年 | 210篇 |
2008年 | 352篇 |
2007年 | 312篇 |
2006年 | 335篇 |
2005年 | 291篇 |
2004年 | 253篇 |
2003年 | 255篇 |
2002年 | 205篇 |
2001年 | 91篇 |
2000年 | 74篇 |
1999年 | 86篇 |
1998年 | 32篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 38篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 71篇 |
1991年 | 61篇 |
1990年 | 48篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 35篇 |
1986年 | 33篇 |
1985年 | 34篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1975年 | 26篇 |
1974年 | 16篇 |
1973年 | 17篇 |
排序方式: 共有5616条查询结果,搜索用时 15 毫秒
21.
A rapid method is described for the preparation of serum alpha1-acid glycoprotein from rats with inflammation induced with turpentine oil injection. The protein obtained by two purification steps, batchwise adsorption with DEAE-cellulose followed by chromatography on CM-cellulose, was proved to be native alpha1-acid glycoprotein in a high degree of purity by electrophoretical, immunological, ultracentrifugal and carbohydrate analysis. The monospecific and potent antiserum to this protein was prepared by immunizing rabbits with the desialyzed material emulsified with Freund's incomplete adjuvant. Using purified alpha1-acid glycoprotein and its specific antiserum, the concentration of alpha1-acid glycoprotein in rat serum was determined by single radial immunodiffusion. Abnormally high levels of its concentration (5-6 times higher than the control) were observed in inflammatory and tumor bearing rats. 相似文献
22.
Specific antisera against somatostatin-28 were prepared by absorption of somatostatin-28 antisera with sepharose 4B-somatostatin-14. Indirect immunofluorescence techniques using somatostatin-14 antisera and specific antisera against somatostatin-28 were carried out to elucidate the time of occurrence of somatostatin-28 in the fetal pancreatic islets and to ascertain whether somatostatin-28 was present in the adult pancreatic islets or not, and further to examine whether cells reacting with specific antisera against somatostatin-28 are identical to those reacting with somatostatin-14 antisera or not. Somatostatin-28 like immunoreactivity occurred in the fetal pancreatic islets at 11th week's gestation and was found in all fetal pancreatic islets examined in the present study. It was also found in the adult pancreatic islets. Furthermore, cells reacting with specific antisera against somatostatin-28 in the fetal and adult pancreatic islets were identical to those reacting with somatostatin-14 antisera. Thus, the present study elucidated the presence of somatostatin-28 like immunoreactivity in the human pancreas. However, it could not be decided whether cells reacting with somatostatin-28 antisera contain either only somatostatin-28 or both somatostatin-28 and somatostatin-14; in other words, whether somatostatin-14 is produced from somatostatin-28 or not, since somatostatin-14 antisera had a cross-reactivity to both somatostatin-14 and somatostatin-28. 相似文献
23.
24.
Shuhichi Takahashi Susumu Kitanaka Michio Takido Ushino Sankawa Shoji Shibata 《Phytochemistry》1977,16(7):999-1002
From seedlings of Cassia torosa four dimeric hydroanthracenes have been isolated. Two, a pair of atropisomeric dimers consisting of two molecules o 相似文献
25.
T Yano C Taura M Shibata Y Hirono S Ando M Kusubata T Takahashi M Inagaki 《Biochemical and biophysical research communications》1991,175(3):1144-1151
Monoclonal antibody YC10 showed specificity for the phosphorylated form of human, bovine and porcine glial fibrillary acidic proteins (GFAPs) and negligible reactivity towards the dephosphorylated form of the GFAPs. Analysis of species specificity and of the epitope, determined using synthetic phosphopeptides, indicated that this antibody recognized the local phosphorylation-site sequence Thr-phosphoSer-Ala-Ala-Arg-Arg (residues 7-12 of GFAP). Making use of this antibody we developed a non-radioactive method to measure protein kinase activities. After incubation of a protein kinase with non-radioactive ATP in ninety-six wells coated with the synthetic peptide Arg-Arg-Arg-Val-Thr-Ser-Ala-Ala-Arg-Arg-Ser-Cys (residues 3-13 of GFAP), the phosphorylated product was detected by using this mouse antibody and peroxidase-labeled goat anti-mouse IgG. This method proved to be equally as sensitive as the radioactive method for the measurement of protein kinase activities and was less affected by concentrations of ATP present in the reaction mixture. 相似文献
26.
27.
Hydroperoxide decomposition by the NADP-glutathione system in rat liver mitochondria was analyzed. Mitochondria were found to contain high concentrations of the reduced form of glutathione (GSH) (4.32 +/- 0.50 nmol/mg) and NADPH (4.74 +/- 0.64 nmol/mg), and high activities of glutathione peroxidase and reductase. In the initial phase of the reaction, the rate of hydroperoxide decomposition was proportional to both the GSH level and the activity of GSH peroxidase. However, in the later steady state, the step of NADP reduction was rate-limiting, and the overall reaction rate was independent of the initial concentration of GSH, and activities of glutathione peroxidase and reductase. Some GSH was released from mitochondria during incubation, but the rate of the decomposition could be simply expressed as kappa [GSH]/2, where kappa is the first-order rate constant of the peroxidase and [GSH] is the intramitochondrial level of GSH in the steady state. The rate of the reaction in the steady state was also dependent on the NADPH level, its reciprocal being linearly correlated with [NADPH]-1. The rate of decomposition of hydroperoxide was influenced by the respiratory state. During state 3 respiration, the rate was greatly depressed, but was still considered to exceed by far the rate of physiological generation of hydroperoxide. 相似文献
28.
The results of a 60 ps molecular dynamics (MD) simulation of (dG)6.(dC)6 including 10 Na+ counterions and 292 water molecules are presented. All backbone angles and helix parameters for the hexamer are reported in this paper along with trajectory plots of selected angles. Hydrogen bonding between the bases along the helical axis was observed to fluctuate with time, showing the dynamic nature of the base-pairing interaction. These fluctuations gave rise to unusual hydrogen-bonding patterns. Good intrastrand base stacking and no interstrand base stacking were also observed. The hexamer minihelix retains an essentially B-DNA conformation throughout the entire simulation even though some helix parameters and backbone angles do not have strict B-DNA values. The most striking feature obtained from the simulation was a high propeller twist, which resulted in a narrow minor groove for the minihelix. It is proposed that (dG)n.(dC)n sequences are resistant to DNAase I because of this narrow minor groove in dilute aqueous solution. 相似文献
29.
Shukuko Ikawa Takehiko Shibata Tadahiko Ando Hiuga Saito 《Molecular & general genetics : MGG》1980,177(3):359-368
Summary We transformed B. subtilis 168 with DNA from B. subtilis IAM1231, IAM1192 and ATCC6633. When we examined the restriction activities of the transformants in vivo and in vitro using phage 105C we found the following: (1) Cells of either IAM1231 or IAM1192 have two modification and restriction systems (Bsu1231(1)-system and Bsu1231(II)-system in IAM1231, and Bsu1192(I)-system and Bsu1192(II)-systems in IAM1192), and cells of ATCC6633 have only one system (Bsu6633-system). (2) The restriction enzymes of all of these five systems are site-specific endonucleases. (3) The nucleotide sequence specificities of the enzymes involved in Bsu1231(I)-system, Bsu1192(I)-system and Bsu6633-system are the same; and those of Bsu1231(II)-system and Bsu1192(II)-system are the same. The sequence specificities of these two groups are different from each other and also different from those of the Bsu168-system of B. subtilis 168, the BsuR-system of B. subtilis R and the Bsu1247(I)-and Bsu1247(II)-systems which are systems of B. subtilis IAM1247. (4) Transformants possessing four different modification and restriction systems (Bsu1231(I)-, Bsu1247(I)-, BsuR- and Bsu168-systems) were constructed. (5) Transformation of two derivatives of 168 that were m
R
+
r
R
+
by DNA from IAM1231 produced 16 transformants that had the Bsu1231(II) restriction system, but had lost the BsuR system. Transformation of a derivative of 168 that was m
1247(II)
+
r
1247(II)
+
by DNA from m
1231(II)
+
r
1231(II)
+
-or m
R
+
r
R
+
-derivative of 168 produced about 100 each of transformants that had the Bsu1231(II)-restriction system or the BsuR-restriction system. But all these transformants lost the Bsu1247(II)-system. 相似文献
30.
Yasuaki Yanagawa Rieko Shimogawara Misao Takano Takahiro Aoki Daisuke Mizushima Hiroyuki Gatanaga Yoshimi Kikuchi Shinichi Oka Kenji Yagita Koji Watanabe 《PLoS neglected tropical diseases》2022,16(4)
BackgroundAmebiasis, caused by Entamoeba histolytica, is spreading in developing countries and in many developed countries as a sexually transmitted infection. Here, we evaluated the efficacy of serological screening to identify asymptomatic E. histolytica infection as a potential epidemiological control measure to limit its spread.Methodology/Principal findingsThis cross-sectional study was carried out between January and March 2021 in an HIV-negative men who have sex with men (MSM) cohort at the National Center for Global Health and Medicine. Serological screening was performed using a commercially available ELISA kit. For seropositive individuals, we performed stool polymerase chain reaction (PCR) to determine current E. histolytica infection. We performed E. histolytica serological screening of 312 participants. None had a history of E. histolytica infection prior to the study. The overall E. histolytica seropositivity was 6.7% (21/312), which was similar to that found by the rapid plasma reagin test (17/312). We identified current infection in 8 of 20 seropositive participants (40.0%) by stool PCR.Conclusions/SignificanceOur serological screening approach constitutes a potentially practical epidemiological strategy. Active epidemiological surveys, in combination with an effective screening strategy for asymptomatically infected individuals, should be applied to help reduce sexually transmitted E. histolytica infections. 相似文献