全文获取类型
收费全文 | 2650篇 |
免费 | 185篇 |
出版年
2022年 | 12篇 |
2021年 | 28篇 |
2020年 | 12篇 |
2019年 | 22篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 45篇 |
2015年 | 77篇 |
2014年 | 101篇 |
2013年 | 140篇 |
2012年 | 124篇 |
2011年 | 113篇 |
2010年 | 87篇 |
2009年 | 76篇 |
2008年 | 124篇 |
2007年 | 132篇 |
2006年 | 108篇 |
2005年 | 131篇 |
2004年 | 128篇 |
2003年 | 123篇 |
2002年 | 123篇 |
2001年 | 91篇 |
2000年 | 105篇 |
1999年 | 82篇 |
1998年 | 31篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 31篇 |
1992年 | 77篇 |
1991年 | 63篇 |
1990年 | 48篇 |
1989年 | 44篇 |
1988年 | 42篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 36篇 |
1984年 | 33篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1976年 | 13篇 |
1973年 | 11篇 |
1972年 | 14篇 |
1971年 | 11篇 |
1970年 | 13篇 |
1969年 | 14篇 |
排序方式: 共有2835条查询结果,搜索用时 15 毫秒
1.
Young-Jun Park Tomotaro Nishikawa Norihiko Tomooka Kazuhiro Nemoto 《Molecular breeding : new strategies in plant improvement》2012,30(1):511-520
Polymorphisms at the Waxy locus of Amaranthus caudatus L. collected from a wide range of regions were used to investigate genetic diversity and mutation sites. A comparison of the Waxy locus revealed a very high level of sequence conservation. This result clearly showed low environmental and evolutionary variability in the Waxy gene. We also performed screening to confirm the mutation sites in the coding sequences of all accessions. The results indicate that one insertion in the coding region of Waxy genes was responsible for the change in perisperm starch leading to the waxy phenotype in all accessions of this species, and thus that a single mutation event altered the regulation of the Waxy gene during the domestication of this crop. In addition, phylogenetic analysis showed that waxy phenotypes within each of three species, A. caudatus, A. cruentus and A. hypochondriacus, originated separately or differentiated from nonwaxy phenotypes of each species through a single mutational event (i.e., a frame shift or base substitution). We also compared obvious structural features of the coding sequence of waxy and nonwaxy phenotypes with those of low-amylose phenotypes in A. caudatus. The Waxy coding sequences of low-amylose phenotypes do not show polymorphisms and are identical with those of waxy phenotypes. This could mean that there is another gene that encodes a key enzyme responsible for amylose synthesis as the elementary quantity in tissues other than perisperm in A. caudatus. 相似文献
2.
Chemical taxonomy of the hinge-ligament proteins of bivalves according to their amino acid compositions. 总被引:1,自引:0,他引:1 下载免费PDF全文
The proteins in the hinge ligaments of molluscan bivalves were subjected to chemotaxonomic studies according to their amino acid compositions. The hinge-ligament protein is a new class of structure proteins, and this is the first attempt to introduce chemical taxonomy into the systematics of bivalves. The hinge-ligament proteins from morphologically close species, namely mactra (superfamily Mactracea) or scallop (family Pectinidae) species, showed high intraspecific homology in their compositions. On the other hand, inconsistent results were obtained with two types of ligament proteins in pearl oyster species (genus Pinctada). The results of our chemotaxonomic analyses were sometimes in good agreement with the morphological classifications and sometimes inconsistent, implying a complicated phylogenetic relationship among the species. 相似文献
3.
M. P. De Leon T. Yanagi M. Kikuchi J. Mu O. Ayau V. Matta M. Paz S. Juarez H. Kanbara I. Tada K. Hirayama 《International journal for parasitology》1998,28(12):1867-1874
Fifty fresh isolates of Trypanosoma cruzi from Triatoma dimidiata vectors and 31 from patients with Chagas disease were analysed for DNA polymorphisms within the 432-bp core region of the cruzipain gene which encodes the active site of cathepsin L-like cystein proteinase. The cruzipain gene showed signs of polymorphism consisting of four different DNA sequences in Central and South American isolates of T. cruzi. The PCR fragments of Guatemalan isolates could be divided into three groups, Groups 1, 2 and 3, based on different patterns of single-stranded DNA conformation polymorphism. All of the strains isolated from Brazil, Chile, and Paraguay, except for the CL strain, showed a Group 4 pattern. Two to four isolates from each group were analysed by cloning and sequencing. A silent mutation occurred between Groups 1 and 2, and five nucleotides and two aa substitutions were detected between Groups 1 and 3. The DNA sequence of Group 4 contained five nucleotides and one aa substitution from Group 1. All of the DNA sequences corresponded well with the single-stranded DNA conformation polymorphism. The Group 1 isolates, the majority in the Guatemalan population (70/81, 86.4%), were isolated from both triatomines and humans, but Group 3 were isolated only from humans. Moreover, the Group 2 isolates were detected only in triatomine vectors (9/50; 18%), but never in humans (0/32, P<0.05) suggesting that this group has an independent life-cycle in sylvatic animals and is maintained by reservoir hosts other than humans. 相似文献
4.
5.
Beh?et's disease is characterized by recurrent aphthous stomatitis, uveitis, genital ulcers, and skin lesions. The role of
the HLA-B*51 gene has been confirmed in recent years, although its contribution to the overall genetic susceptibility to Beh?et's disease
was estimated to be only 19%. The production of a variety of cytokines by T cells activated with multiple antigens has been
shown to play a pivotal role in the activation of neutrophils. As regards the treatment, anti-tumor necrosis factor alpha
therapy has been shown to be effective for mucocutaneous symptoms as well as for sight-threatening panuveitis, although a
randomized, controlled trial is required. 相似文献
6.
Jun Iwaki Kunio Kikuchi Yoshiaki Mizuguchi Yutaka Kawahigashi Hiroshi Yoshida Eiji Uchida Toshihiro Takizawa 《PloS one》2013,8(7)
MicroRNA miR-376c was expressed in normal intrahepatic biliary epithelial cells (HIBEpiC), but was significantly suppressed in the HuCCT1 intrahepatic cholangiocarcinoma (ICC) cell line. The biological significance of the down-regulation of miR-376c in HuCCT1 cells is unknown. We hypothesized that miR-376c could function as a tumor suppressor in these cells. To test this hypothesis, we sought the targets of miR-376c, and characterized the effect of its down-regulation on HuCCT1 cells. We performed proteomic analysis of miR-376c-overexpressing HuCCT1 cells to identify candidate targets of miR-376c, and validated these targets by 3′-UTR reporter assay. Transwell migration assays were performed to study the migratory response of HuCCT1 cells to miR-376c overexpression. Furthermore, microarrays were used to identify the signaling that were potentially involved in the miR-376c-modulated migration of HuCCT1. Finally, we assessed epigenetic changes within the potential promoter region of the miR-376c gene in these cells. Proteomic analysis and subsequent validation assays showed that growth factor receptor-bound protein 2 (GRB2) was a direct target of miR-376c. The transwell migration assay revealed that miR-376c significantly reduced epidermal growth factor (EGF)-dependent cell migration in HuCCT1 cells. DNA microarray and subsequent pathway analysis showed that interleukin 1 beta and matrix metallopeptidase 9 were possible participants in EGF-dependent migration of HuCCT1 cells. Bisulfite sequencing showed higher methylation levels of CpG sites upstream of the miR-376c gene in HuCCT1 relative to HIBEpiC cells. Combined treatment with the DNA-demethylating agent 5-aza-2′-deoxycytidine and the histone deacetylase inhibitor trichostatin A significantly upregulated the expression of miR-376c in HuCCT1 cells. We revealed that epigenetic repression of miR-376c accelerated EGF-dependent cell migration through its target GRB2 in HuCCT1 cells. These findings suggest that miR-376c functions as a tumor suppressor. Since metastasis is the major cause of death in ICC, microRNA manipulation could lead to the development of novel anti-cancer therapy strategies for ICC. 相似文献
7.
8.
The characteristics of phosphate transport across intestinal basolateral membranes of the rat were determined by using enriched preparations in which uphill Na+-dependent D-glucose transport could not be demonstrated, but ATP-dependent Ca2+ transport was present. Phosphate transport was saturable, Na+-dependent and exhibited Michaelis-Menten kinetics. Vmax. was 51.1 +/- 4.2 pmol/10 s per mg of protein and Km was 14 +/- 3.9 microM. The transport process was electroneutral. Tracer-exchange experiments and counter-transport studies confirmed the presence of a Na+-Pi carrier at the basolateral membrane. The presence of inside-positive membrane potential did not enhance phosphate uptake, indicating that the Na+ effect is secondary to the presence of the Na+-Pi carrier rather than an induction of positive membrane potential. The stoichiometry of this carrier at pH 7.4 was 2 Na+:1 phosphate, as shown by direct studies utilizing the static-head method. These studies are the first to determine the presence of a phosphate carrier at the basolateral membrane. 相似文献
9.
Genetic mechanisms of tumor-specific loss of 11p DNA sequences in Wilms tumor. 总被引:12,自引:7,他引:5 下载免费PDF全文
D D Dao W T Schroeder L Y Chao H Kikuchi L C Strong V M Riccardi S Pathak W W Nichols W H Lewis G F Saunders 《American journal of human genetics》1987,41(2):202-217
Wilms tumor, a common childhood renal tumor, occurs in both a heritable and a nonheritable form. The heritable form may occasionally be attributed to a chromosome deletion at 11p13, and tumors from patients with normal constitutional chromosomes often show deletion or rearrangement of 11p13. It has been suggested that a germinal or somatic mutation may occur on one chromosome 11 and predispose to Wilms tumor and that a subsequent somatic genetic event on the normal homologue at 11p13 may permit tumor development. To study the frequency and mechanism of such tumor-specific genetic events, we have examined the karyotype and chromosome 11 genotype of normal and tumor tissues from 13 childhood renal tumor patients with different histologic tumor types and associated clinical conditions. Tumors of eight of the 12 Wilms tumor patients, including all viable tumors examined directly, show molecular evidence of loss of 11p DNA sequences by somatic recombination (four cases), chromosome loss (two cases), and recombination (two cases) or chromosome loss and duplication. One malignant rhabdoid tumor in a patient heterozygous for multiple 11p markers did not show any tumor-specific 11p alteration. These findings confirm the critical role of 11p sequences in Wilms tumor development and reveal that mitotic recombination may be the most frequent mechanism by which tumors develop. 相似文献
10.
Dr. Shuichi Ueda Toshikuni Tanabe Norihiko Ihara Yutaka Sano 《Cell and tissue research》1989,256(3):457-463
Summary Pieces of fetal midbrain raphe containing serotonergic and dopaminergic neurons were transplanted into the leptomeningeal tissue (see Fig. 3) of adult host rats that had previously been denervated by treatment with 5,6-dihydroxytryptamine. One, 2 and 5 months after transplantation, the rate of neuronal survival in the grafted tissue and the extent of axonal outgrowth into the host brain were studied by use of serotonin and tyrosine hydroxylase (TH) immunohistochemistry. The survival rate of the grafts in the 1-month group was approximately 70%. Neurons containing either serotonin or catecholamine were demonstrated by means of immunocytochemical procedures in the grafts. Two and 5 months after transplantation, serotonin-immunoreactive nerve fibers were densely distributed throughout the graft tissue, while TH-immunoreactive fiber elements were restricted to an area near the somata of TH-positive neurons. Numerous serotonin-immunoreactive fibers derived from the transplant were found in the leptomeningeal tissue surrounding the graft, on the wall of neighboring blood vessels, and also in the adjacent parenchyma of the host brain. Outgrowing TH-immunoreactive nerve fibers were not observed in the host brain, although such elements occurred in the leptomeningeal tissue and the wall of the larger blood vessels. These results suggest that the serotonergic and catecholaminergic (dopaminergic) neurons located in transplants of the raphe nuclei show different patterns when reinnervating the host tissue. 相似文献