全文获取类型
收费全文 | 7376篇 |
免费 | 528篇 |
国内免费 | 4篇 |
专业分类
7908篇 |
出版年
2021年 | 62篇 |
2020年 | 40篇 |
2019年 | 53篇 |
2018年 | 88篇 |
2017年 | 60篇 |
2016年 | 90篇 |
2015年 | 171篇 |
2014年 | 208篇 |
2013年 | 456篇 |
2012年 | 311篇 |
2011年 | 309篇 |
2010年 | 212篇 |
2009年 | 204篇 |
2008年 | 311篇 |
2007年 | 338篇 |
2006年 | 291篇 |
2005年 | 310篇 |
2004年 | 313篇 |
2003年 | 300篇 |
2002年 | 296篇 |
2001年 | 268篇 |
2000年 | 271篇 |
1999年 | 240篇 |
1998年 | 110篇 |
1997年 | 92篇 |
1996年 | 81篇 |
1995年 | 86篇 |
1994年 | 86篇 |
1993年 | 88篇 |
1992年 | 180篇 |
1991年 | 146篇 |
1990年 | 159篇 |
1989年 | 161篇 |
1988年 | 129篇 |
1987年 | 145篇 |
1986年 | 99篇 |
1985年 | 132篇 |
1984年 | 110篇 |
1983年 | 83篇 |
1982年 | 69篇 |
1981年 | 56篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 42篇 |
1977年 | 58篇 |
1976年 | 40篇 |
1975年 | 39篇 |
1974年 | 52篇 |
1973年 | 48篇 |
1970年 | 57篇 |
排序方式: 共有7908条查询结果,搜索用时 15 毫秒
41.
Carboxyl-terminal deletion analysis of the Streptococcus mutans glucosyltransferase-I enzyme 总被引:9,自引:0,他引:9
Sequential deletion of the carboxyl-terminal amino acids (including the six direct repeating units) of the glucosyltransferase-I (GTF-I) enzyme of Streptococcus mutans revealed differential effects on sucrase and GTF activities. Removal of all but one repeating unit resulted in a truncated enzyme with significant sucrase activity but no detectable GTF activity. These results are compatible with the presence of two functional domains in the enzyme. 相似文献
42.
The vascular anatomy ofHelminthostachys zeylanica was examined with special reference to anomalous secondary tissue. Primary xylem development gradually takes place centrifugally. In branched rhizomes with destroyed apices, the vascular cylinder apical to the insertion of branch traces is generally composed of primary xylem, accessory xylem, inner parenchyma of radially arranged cells, outer parenchyma of irregularly arranged cells, and partly crushed phloem, listed in order going outwards. The accessory xylem as well as the inner parenchyma ofHelminthostachys zeylanica is probably secondarily produced, partly to contribute to the branch traces, in a position corresponding to that of secondary vascular tissue developed from a normal cambium inBotrychium sensu lato. It is suggested that although a cambium is lacking inHelminthostachys zeylanica, the secondary vascular tissues are comparable between the genera. The phylogenetic implication of this tissue is discussed. 相似文献
43.
The polymerase chain reaction for Mycoplasma pulmonis 总被引:2,自引:0,他引:2
R Harasawa K Koshimizu T Uemori O Takeda K Asada I Kato 《Microbiology and immunology》1990,34(4):393-395
In vitro DNA amplification by polymerase chain reaction was examined to detect Mycoplasma pulmonis. A pair of synthetic oligonucleotide primers was constructed, and used to amplify a unique sequence of M. pulmonis DNA. Amplified products were detected by agarose gel electrophoresis and verified by blot hybridization with a synthetic oligonucleotide probe. This system detected cellular DNA of M. pulmonis but not M. arthritidis or M. neurolyticum, and thus appears to be useful for M. pulmonis diagnosis. 相似文献
44.
K Yamashita A Umemoto S Grivas S Kato S Sato T Sugimura 《Nucleic acids symposium series》1988,(19):111-114
DNA adducts formed by 12 heterocyclic amines were analyzed by 32P-postlabeling method. Several DNA adducts were detected in rat liver by administration of each heterocyclic amine. Total adduct levels ranged from 0.5 for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to more than 250 for 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) per 10(7) nucleotides 24 hr after intragastric administration of these compounds. The N-hydroxy derivative of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was reactive toward DNA in vitro to form adducts. Addition of acetic anhydride to N-OH-MeIQx greatly enhanced its reactivity to DNA. 32P-Postlabeling analysis revealed that the MeIQx-DNA adducts formed in vivo and in vitro were identical. Thus, MeIQx would be metabolized in vivo to N-hydroxy form and further esterified to produce more reactive species, such as N-acetoxy form, which modify DNA to form adducts. 相似文献
45.
The heterogeneity of rat kidney lysosomes revealed by immunoelectron microscopic staining for cathepsins B and H 总被引:1,自引:0,他引:1
The heterogeneity of lysosomes was studied by analyzing the immunostaining behavior of cathepsins B and H in rat kidney proximal tubule cells. Rat kidneys were fixed by perfusion and embedded in Lowicryl K4M. A protein A-gold technique was applied to serial sections and a double labeling technique to conventional sections. By analyzing the immunostaining behavior of cathepsins B and H in the same lysosomes which were cut into separate sections, four types of lysosomes were found: Type 1 positive for both proteinases; type 2 strongly positive for cathepsin B, but weakly or negative for cathepsin H; type 3 strongly positive for cathepsin H, but weakly or negative for cathepsin B; and type 4 negative for both proteinases. The double labeling by two different sizes of the protein A-gold probes showed these four types of lysosomes. The results indicate that there exists the lysosomal heterogeneity of the proteinase content in the kidney proximal tubule cells. 相似文献
46.
Nobuo Kato Sumiko Mizuno Yukio Imada Masayuki Shimao Chikahiro Sakazawa 《Applied microbiology and biotechnology》1988,27(5-6):567-571
Summary Formaldehyde dismutase was greatly stabilized by immobilization in a urethane prepolymer (PU-6). The immobilized enzyme exhibited stochiometrical dismutation of formaldehyde to methanol and formate in several repeated reactions. Conversion of methanol to formate occurred in a reaction with an immobilized enzyme system consisting of alcohol oxidase, catalase and formaldehyde dismutase, and with an intact cell-mixture of Hansenula polymorpha and Pseudomonas putida. Furthermore, the stability of the cell-mixture during repeated reactions was greatly improved by the immobilization, the 600 mM methanol added periodically being converted to formate in a 75% yield in 12 h. The immobilized cellsystem was also effective for the conversion of several aliphatic alcohols, C1 to C4, to the corresponding acids. 相似文献
47.
Sachiko Aono Hiroshi Sato Reiji Semba Shigeo Kashiwamata Kanefusa Kato † Lawrence F. Eng† 《Journal of neurochemistry》1988,50(3):717-721
The behavior of marker proteins of glial cells [alpha-enolase, beta-S100 protein, and glial fibrillary acidic protein (GFAP)] was investigated quantitatively by using enzyme immunoassay systems during the development of cerebellar hypoplasia in jaundiced Gunn rats. A neuronal marker protein, gamma-enolase, was also measured as a reference. At postnatal day 8 corresponding to the early stage of cerebellar damage, the amount of beta-S100 on a protein basis was significantly higher in jaundiced homozygotes (jj) than in control nonjaundiced heterozygotes (j+), whereas no differences in alpha- and gamma-enolases and GFAP were observed between the two groups of rats. At days 15 and 30, which correspond, respectively, to the advanced and late stages of cerebellar damage, the three glial proteins, especially GFAP, were higher and the neuronal protein was lower in the jj rat cerebellum than in the control. These results are consistent with the reported histological observations that neuronal cells are vulnerable and damaged by bilirubin, whereas glial cells seem to be less sensitive. On the other hand, the amounts of beta-S100 and alpha-enolase per cerebellum were significantly lower in jj rats at days 15 and 30, as in the case of gamma-enolase, whereas that of GFAP remained at the same level as the control at day 15 and showed a slight but significant decrease at day 30. The possibility is suggested that beta-S100 and GFAP may be available as biochemical indicators of glial cells, especially in the early and advanced stages of cerebellar damage, respectively, but that alpha-enolase is less available. 相似文献
48.
Kato Yoji; Otsuki Tatsuya; Nakajima Tasuku; Ojima Kunihiko; Matsuda Kazuo 《Plant & cell physiology》1988,29(4):539-547
-Glucans (average mol wt, 1.3 ? 104) extracted with perchloricacid from 8-day-old suspension-cultured nonglutinous (var. Sasanishiki)and glutinous rice (var. Miyakogane) cells were compared. Theresults of hydrolysis by alpha;-, ß- and iso-amylasesand methylation analysis of the -glucans suggested that theirbasic structures are almost the same. These -glucans are highly-branchedpolysaccharides with an average chain length of about 910,with exterior and interior chain lengths of about 67and 23, respectively.
1Current address: Laboratory of Food Science, Faculty of Education,Hirosaki University, Hirosaki, Aomori 036, Japan. (Received April 27, 1987; Accepted March 2, 1988) 相似文献
49.
We previously reported that human promyelocytic leukemia HL-60 cells, when treated with various inducers in magnesium-deficient medium, became committed to differentiate but did not express the differentiation-related phenotypes (Okazaki et al., J. Cell. Physiol., 131:50-57, 1987). In the present study we demonstrated the existence of an intracellular differentiation-inducing activity (int-DIA) in differentiation-committed phenotype-nonexpressing HL-60 cells by using cybrid formation between untreated HL-60 cells and cytoplasts from HL-60 cells treated in magnesium-deficient medium with 100 nM 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3). Cell extracts from similarly treated HL-60 cells also showed int-DIA, which when added (10 mg total protein/ml) to culture of untreated HL-60 cells, could increase the percentages of nitroblue tetrazolium (NBT)- and nonspecific esterase (NSE)-positive cells from 1% to 53%, and from 0 to 32%, respectively. They also induced differentiation of human monoblastic leukemia U-937 cells and of human myeloblastic leukemia KG-1 cells but not of erythroleukemia K-562 cells. These results suggested that the int-DIA had a common effect on differentiation induction in several human myeloid cell lines and may be involved in inducing cells to proceed from a commitment to a phenotype-expression step during human myeloid cell differentiation. 相似文献
50.
Effect of taurine on growth hormone and prolactin secretion in rats: possible interaction with opioid peptidergic system 总被引:1,自引:0,他引:1
The effect of taurine on growth hormone (GH) and prolactin (PRL) secretion was investigated in the urethane-alpha-chloralose anesthetized rats, considering the interaction with endogenous opioid peptidergic system. Intraventricular injection of taurine (0.25 and 1.0 mumol) stimulated GH and PRL secretion in a dose-dependent manner. However, 4.0 mumol taurine failed to show these effect. The intravenous infusion of naloxone (4 mg/kg b.w.) completely inhibited both the GH and PRL secretion induced by taurine (1.0 mumol). The combined treatment of taurine (1.0 mumol) and FK33-824 (Met-enkephalin derivative, 100 micrograms/kg b.w., i.v.) significantly increased GH and PRL responses induced by taurine or FK33-824 alone. These results indicate that taurine is an effective stimulator of GH and PRL secretion in rats, and that the mechanism of this action involves the opioid peptidergic system in the hypothalamus. 相似文献