全文获取类型
收费全文 | 19125篇 |
免费 | 1205篇 |
国内免费 | 4篇 |
出版年
2022年 | 114篇 |
2021年 | 225篇 |
2020年 | 119篇 |
2019年 | 152篇 |
2018年 | 231篇 |
2017年 | 183篇 |
2016年 | 337篇 |
2015年 | 503篇 |
2014年 | 583篇 |
2013年 | 1192篇 |
2012年 | 1022篇 |
2011年 | 979篇 |
2010年 | 585篇 |
2009年 | 632篇 |
2008年 | 1004篇 |
2007年 | 959篇 |
2006年 | 958篇 |
2005年 | 967篇 |
2004年 | 1014篇 |
2003年 | 949篇 |
2002年 | 847篇 |
2001年 | 588篇 |
2000年 | 566篇 |
1999年 | 481篇 |
1998年 | 237篇 |
1997年 | 205篇 |
1996年 | 177篇 |
1995年 | 158篇 |
1994年 | 168篇 |
1993年 | 159篇 |
1992年 | 360篇 |
1991年 | 319篇 |
1990年 | 326篇 |
1989年 | 302篇 |
1988年 | 251篇 |
1987年 | 253篇 |
1986年 | 225篇 |
1985年 | 194篇 |
1984年 | 150篇 |
1983年 | 144篇 |
1982年 | 134篇 |
1981年 | 128篇 |
1980年 | 99篇 |
1979年 | 123篇 |
1978年 | 97篇 |
1977年 | 89篇 |
1976年 | 87篇 |
1975年 | 75篇 |
1974年 | 91篇 |
1973年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Detection of fimbriae and fimbrial antigens on the oral anaerobe Bacteroides gingivalis by negative staining and serological methods 总被引:6,自引:0,他引:6
Y Suzuki F Yoshimura K Takahashi H Tani T Suzuki 《Journal of general microbiology》1988,134(10):2713-2720
We screened 63 clinical isolates of Bacteroides gingivalis from eight different laboratories for the presence of fimbriae by negative staining and by immunological methods. Techniques used were bacterial agglutination, Ouchterlony immunodiffusion and Western immunoblotting analysis using rabbit anti-fimbriae and anti-fimbrilin sera raised against fimbriae and fimbrilin (a constituent protein of B. gingivalis fimbriae) from B. gingivalis strain 381. In 49 of the 51 strains tested, fimbriae were clearly detected by negative staining, and 30 (60%) of the fimbriate strains were positive in all three of the immunological assays. A total of 37 strains (75%) were positive by immunoblotting analysis, which was the most reliable of the serological methods used in this study. The study shows that the majority of B. gingivalis strains are fimbriate, and that these fimbriae are immunologically related to the fimbriae of B. gingivalis strain 381. Molecular heterogeneity of fimbrilin was discovered by the immunoblotting analysis, when different strains were compared. With most of the strains, including strain 381, the antifimbrilin serum reacted with a protein of apparent molecular mass 43 kDa, but with 15 strains the immuno-reactive protein had an apparent molecular mass of 46 kDa. 相似文献
92.
Dual regulation of resistance against Toxoplasma gondii infection by Lyt-2+ and Lyt-1+, L3T4+ T cells in mice 总被引:29,自引:0,他引:29
Studies were performed to attempt to define the T cell subset responsible for resistance to Toxoplasma gondii. A temperature-sensitive mutant (ts-4) strain of T. gondii was used for immunization because it causes infection but does not persist in the host. Immunization with this strain induced marked resistance against lethal challenge infection with virulent strains of T. gondii in mice. The resistance could be transferred to normal recipient mice by i.v. injection of spleen cells from ts-4-immunized mice. Marked inhibition of cyst formation in the recipient mice was also noted. The protective activity of immune spleen cells was removed by pretreatment of the spleen cells with anti-Thy-1.2 and C, indicating that T cells are responsible for the observed protection. Pretreatment of immune spleen cells with anti-Lyt-2.2 and C completely ablated their protective effect; pretreatment with anti-Lyt-1.2 or anti-L3T4 and C had lesser effects on their ability to transfer resistance. The effect of anti-Lyt-1.2 was the same as that obtained with anti-L3T4. This suggested that one T cell subset that is partially responsible for protection has both Lyt-1.2 and L3T4 markers on the cell surface. These results indicate that there are substantial roles for both the Lyt-2+ and Lyt-1+, L3T4 T cell subsets in dual regulation of resistance against toxoplasma infection and that Lyt-2+ T cells are the principal mediator of the resistance. 相似文献
93.
NaF-induced Ca2+ mobilization is dependent upon the culture density in a parathyroid hormone-responsive osteoblast-like cell line 总被引:2,自引:0,他引:2
The effect of NaF on cytosolic free Ca2+ concentrations [( Ca2+]i) was examined in a clonal osteoblast-like cell line (MOB 3-4) loaded with Fura 2. MOB 3-4 cells in a sparse culture, which exhibited neither alkaline phosphatase (ALP) activity nor the response to parathyroid hormone (PTH), responded to NaF (0.1-10 mM) to increase [Ca2+]i transiently. In contrast, the cells in a dense culture, which exhibited both ALP activity and the response to PTH, responded to NaF (above 4 mM) to increase [Ca2+]i slowly. [Ca2+]i in osteoblasts in primary culture slowly increased in response to both NaF (above 4 mM) and PTH (3 U/ml). Thus, the sensitivity and the response of MOB 3-4 cells to NaF and PTH varied with the culture density, and high culture density matured the cells like osteoblasts in primary culture. These NaF-induced Ca2+ mobilizations were not dependent upon external Ca2+ and were enhanced by Al3+ (1 microM), whereas the PTH-induced Ca2+ mobilizations were due to Ca2+ influx. These results suggest that the maturation of MOB 3-4 cells, dependent upon the culture density, modulates intracellular signal transduction pathways and thereby alters the NaF-induced Ca2+ mobilization, and that the culture density must be taken into consideration in studying Ca2+ mobilization in such an osteoblast-like cells line as MOB 3-4 cell line. 相似文献
94.
Shin-Ichi Hayama Rika Akamatsu Mayumi Kishimoto Masatsugu Suzuki Hideo Nigi 《Primates; journal of primatology》1988,29(3):423-426
Diverticular disease of the colon was detected in a female Japanese monkey by X-ray examination. The monkey was 15 years old
and had been kept under captive conditions for nine years. Lack of appetite and activity, and constipation were observed.
The monkey was given fiber-rich vegetables and wild plants, and its appetite and activity then improved. Based on a consideration
of various factors, it is suggested that one possible cause of the diverticulosis in this case was a low dietary fiber intake. 相似文献
95.
Studies of Sl/Sld in equilibrium with +/+ mouse aggregation chimaeras. II. Effect of the steel locus on spermatogenesis 总被引:3,自引:0,他引:3
H Nakayama H Kuroda H Onoue J Fujita Y Nishimune K Matsumoto T Nagano F Suzuki Y Kitamura 《Development (Cambridge, England)》1988,102(1):117-126
Mutant mice of Sl/Sld genotype are deficient in melanocytes, erythrocytes, mast cells and germ cells. Deficiency of melanocytes, erythrocytes and mast cells is not attributable to an intrinsic defect in their precursor cells but to a defect in the tissue environment that is necessary for migration, proliferation and/or differentiation. We investigated the mechanism of germ cell deficiency in male Sl/Sld mice by producing aggregation chimaeras from Sl/Sld and +/+ embryos. Chimaeric mice with apparent white stripes were obtained. Two of four such chimaeras were fertile and the phenotypes of resulting progenies showed that some Sl/Sld germ cells had differentiated into functioning sperms in the testis of the chimaeras. In cross sections of the testes of chimaeras, both differentiated and nondifferentiated tubules were observed. However, the proportions of type A spermatogonia to Sertoli cells in both types of tubules were comparable to the values observed in differentiated tubules of normal +/+ mice. We reconstructed the whole length of four tubules from serial sections. Differentiated and nondifferentiated segments alternated in a single tubule. The shortest differentiated segment contained about 180 Sertoli cells and the shortest nondifferentiated segment about 150 Sertoli cells. These results suggest that Sertoli cells of either Sl/Sld or +/+ genotype make discrete patches and that differentiation of type A spermatogonia does not occur in patches of Sl/Sld Sertoli cells. 相似文献
96.
97.
Ischemic insult induces neuronal death in the CA1 subfields of the hippocampus which are designated generally as the most vulnerable brain region. Recent studies have shown that acidic and basic fibroblast growth factors are potent trophic factors that support the survival of neurons in many brain regions including the hippocampus. Here we demonstrate that continuous infusion of acidic fibroblast growth factor into the lateral cerebral ventricles beginning 2 days before ischemia prevents the death of the CA1 pyramidal cells in the hippocampus of gerbils. Furthermore, delayed continuous administration of acidic fibroblast growth factor starting 5 min after ischemia is equally protective. The results suggest a possible physiological function for acidic fibroblast growth factor in the normal support of hippocampal CA1 pyramidal cells and neurons in some other brain regions in considering the broad spectrum of responsive neurons. 相似文献
98.
A new member of the protein kinase C family, nPKC theta, predominantly expressed in skeletal muscle. 下载免费PDF全文
S Osada K Mizuno T C Saido K Suzuki T Kuroki S Ohno 《Molecular and cellular biology》1992,12(9):3930-3938
A new protein kinase C (PKC)-related cDNA with unique tissue distribution has been isolated and characterized. This cDNA encodes a protein, nPKC theta, which consists of 707 amino acid residues and showed the highest sequence similarity to nPKC delta (67.0% in total). nPKC theta has a zinc-finger-like cysteine-rich sequence (C1 region) and a protein kinase domain sequence (C3 region), both of which are common in all PKC family members. However, nPKC theta lacks a putative Ca2+ binding region (C2 region) that is seen only in the conventional PKC subfamily (cPKC alpha, -beta I, -beta II, and -gamma) but not in the novel PKC subfamily (nPKC delta, -epsilon, -zeta, and -eta). Northern (RNA) blot analyses revealed that the mRNA for nPKC theta is expressed predominantly in skeletal muscle. Furthermore, nPKC theta mRNA is the most abundantly expressed PKC isoform in skeletal muscle among the nine PKC family members. nPKC theta expressed in COS1 cells serves as a phorbol ester receptor. By the use of an antipeptide antibody specific to the D2-D3 region of the nPKC theta sequence, nPKC theta was recognized as a 79-kDa protein upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis in mouse skeletal muscle extract and also in an extract from COS1 cells transfected with an nPKC theta cDNA expression plasmid. Autophosphorylation of immunoprecipitated nPKC theta was observed; it was enhanced by phosphatidylserine and 12-O-tetradecanoylphorbol-13-acetate but attenuated by the addition of Ca2+. These results clearly demonstrate that nPKC theta should be considered a member of the PKC family of proteins that play crucial roles in the signal transduction pathway. 相似文献
99.
Kunio Takeda Atsuya Shigemura Satoshi Hamada Weicheng Gu Defu Fang Katsushi Sasa Kazuaki Hachiya 《Journal of Protein Chemistry》1992,11(2):187-192
The effect of protein conformations on the reaction rate of Ellman's reagent, 5,5-dithiobis (2-nitrobenzoic acid) (DTNB) with sulfhydryl (SH) groups of proteins was examined. The stopped-flow method was applied to follow the reaction of DTNB with SH group of two proteins, bovine serum albumin (BSA) and ovalbumin (OVA), at various concentrations of guanidine hydrochloride and urea. The rates for both the proteins were faster in guanidine than in urea. The rate sharply depended on the protein conformations, which were monitored by changes of helix contents on the basis of the circular dichroism measurements. The reaction rate of DTNB with SH groups of BSA was maximal around 2 M guanidine and 5 M urea. On the other hand, the reaction rate of DTNB with OVA was maximal at 3.5 M guanidine, while it gradually increased with an increase in the urea concentration. The amount of reactive SH group participating in the reaction with DTNB was also estimated by the absorbance change at 412 nm. The magnitudes of absorbance change for the reaction with free SH groups of OVA at low concentrations of the denaturants were appreciably smaller than those for BSA with one free SH group. Most of the four SH groups of OVA might react with DTNB above 5 M guanidine, although only a part of them did even at 9 M urea. 相似文献
100.