首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   10174篇
  免费   530篇
  国内免费   4篇
  2021年   109篇
  2020年   53篇
  2019年   79篇
  2018年   114篇
  2017年   105篇
  2016年   149篇
  2015年   230篇
  2014年   278篇
  2013年   604篇
  2012年   499篇
  2011年   448篇
  2010年   293篇
  2009年   292篇
  2008年   474篇
  2007年   440篇
  2006年   452篇
  2005年   410篇
  2004年   417篇
  2003年   438篇
  2002年   387篇
  2001年   413篇
  2000年   407篇
  1999年   337篇
  1998年   139篇
  1997年   108篇
  1996年   85篇
  1995年   83篇
  1994年   77篇
  1993年   85篇
  1992年   242篇
  1991年   246篇
  1990年   197篇
  1989年   179篇
  1988年   182篇
  1987年   158篇
  1986年   148篇
  1985年   146篇
  1984年   120篇
  1983年   108篇
  1982年   89篇
  1981年   58篇
  1980年   57篇
  1979年   90篇
  1978年   84篇
  1977年   61篇
  1976年   57篇
  1975年   49篇
  1973年   58篇
  1972年   43篇
  1970年   49篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The genomic DNA and cDNA for a gene encoding a novel trehalose synthase (TSase) catalyzing trehalose synthesis from α-d-glucose 1-phosphate and d-glucose were cloned from a basidiomycete, Grifola frondosa. Nucleotide sequencing showed that the 732-amino-acid TSase-encoding region was separated by eight introns. Consistent with the novelty of TSase, there were no homologous proteins registered in the databases. Recombinant TSase with a histidine tag at the NH2-terminal end, produced in Escherichia coli, showed enzyme activity similar to that purified from the original G. frondosa strain. Incubation of α-d-glucose 1-phosphate and d-glucose in the presence of recombinant TSase generated trehalose, in agreement with the enzymatic property of TSase that the equilibrium lay far in the direction of trehalose synthesis. Received: 12 January 1998 / Received revision: 20 February 1998 / Accepted: 20 March 1998  相似文献   
992.
N-glycans of a recombinant mouse soluble Fc receptor II (sFcRII) expressed in baby hamster kidney cells were released from glycopeptides by digestion with glycoamidase A (from sweet almond), and the reducing ends of the oligosaccharides were reductively aminated with 2-aminopyridine. The derivatized N-glycans were separated and structurally identified by a three-dimensional high-performance liquid chromatography (HPLC) mapping technique on three kinds of HPLC columns [Takahashi, et al. (1995) Anal. Biochem. 226: 139–46]. Eighteen different major N-glycan structures were identified, of which six were neutral (45%), five mono-sialyl (49%), one di-sialyl (4.6%), five tri-sialyl (1.1%), and one tetra-sialyl (0.3%). All N-glycan structures determined were complex type with fucosylation at the N-acetylglucosamine residue of the reducing end, and N-acetylneuraminic acid, when present, was -(2,3)-linked. The existence of a unique structure containing both N-acetylgalactosamine and -(2,3)-N-acetylneuraminic acid residues at the reducing ends, as below, was confirmed by MALDI-TOF mass spectrometry.  相似文献   
993.
Suckling- and estrogen-induced prolactin release from the anterior pituitary is mediated by alpha-melanocyte stimulating hormone (alpha-MSH) secreted by the intermediate lobe of the pituitary in the rat. Melanocortin 5-receptors are expressed in the anterior pituitary and probably mediate the alpha-MSH function. In contrast, the mouse anterior pituitary does not express the receptor. To examine whether or not alpha-MSH regulates prolactin release in mice, we performed cell immunoblot assay using anterior pituitary cells from adult female mice. We found that alpha-MSH acted on mammotrophs (prolactin-secreting cells) and stimulated prolactin release in a dose dependent manner. A series of RT-PCR using oligonucleotide primer pairs specific for each subtypes of melanocortin receptors revealed that the melanocortin 3-receptor is the sole receptor expressed in the mouse anterior pituitary. These results suggest that alpha-MSH-induced prolactin release is mediated by melanocortin 3-receptors in female mice.  相似文献   
994.
We investigated the gene expression of the alpha chain of C4b-binding protein (C4bp alpha) in a variety of tissues, and in liver cell and hepatoma lines. C4bp alpha mRNA was detected in the liver, but not in the other tissues examined. The constitutive gene expression of C4bp alpha by a hepatoma line, HepG2, was significantly augmented by treatment with monocyte-conditioned medium (MoCM), 12-O-tetradecanoylphorbol-13-acetate (TPA), interleukin-6 (IL6) and tumor necrosis factor (TNF) but not by a calcium ionophore (A23187) or interleukin-1 beta (IL1 beta).  相似文献   
995.
Treatment of oxygen-evolving Photosystem II complexes, whichlack light-harvesting chlorophyll a/b proteins, with a seriesof disuccinimidyl esters with different chain lengths yieldeda crosslinked product which consisted of one molecule each ofthe extrinsic 33 kDa and 23 kDa proteins. In addition, crosslinkingbetween the 33 kDa protein and the chlorophyll-carrying 47 kDaprotein and between the 23 kDa and 17 kDa proteins was confirmed.Thus, the three extrinsic proteins are closely associated witheach other to form a complex which is attached to the PS IIreaction center complexes. (Received December 1, 1989; Accepted May 2, 1990)  相似文献   
996.
The synthesis and SAR studies of 3- and 4-substituted 7-hydroxycoumarins as novel 17β-HSD3 inhibitors are discussed. The most potent compounds from this series exhibited low nanomolar inhibitory activity with acceptable selectivity versus other 17β-HSD isoenzymes and nuclear receptors.  相似文献   
997.
Neonatal toxic shock syndrome (TSS)-like exanthematous disease (NTED) is an emerging neonatal infectious disease caused by TSS toxin-1 (TSST-1). Although NTED and TSS are caused by the same superantigenic exotoxin, NTED is less severe than TSS. The mechanism of this reduced severity in NTED has not been elucidated. Thirteen patients with NTED were enrolled in the study. We investigated serum cytokine profile using a cytometric bead array system with a cytokine panel. Expression of Vβ2 and CD45RO in CD4+ T cells was investigated in mononuclear cells by using flowcytometry. Ten patients with other bacterial infections and eight patients without any infections were also enrolled as control groups. The mean serum level of IL-10 was 1209.9 pg/mL in patients with NTED at the time of admission into the study. The other inhibitory cytokine, IL-4, exhibited a minimum level. The high level of IL-10 rapidly decreased within 3–9 days of the onset of NTED. The cytokine profile of NTED, with its high IL-10 level, was clearly different from that of the other bacterial infections. The increased level of IL-10 seems to be related to the reduced severity of NTED. Th2 shift is not thought to be the cause of this IL-10 excretion.  相似文献   
998.
This study describes complete control region sequences of mitochondrial DNA (mtDNA) from 117 Ethiopian cattle from 10 representative populations, in conjunction with the available cattle sequences in GenBank. In total, 79 polymorphic sites were detected, and these defined 81 different haplotypes. The haplotype and nucleotide diversity of Ethiopian cattle did not vary among the populations studied. All mtDNA sequences from Ethiopian cattle converged into one main maternal lineage (T1) that corresponds to African Bos taurus cattle. According to the results of this study, no zebu mtDNA haplotypes have been found in Ethiopia, where the most extensive hybridization took place on the African continent.  相似文献   
999.
Psychophysiological markers have been focused to investigate the psychopathology of psychiatric disorders and personality subtypes. In order to understand neurobiological mechanisms underlying these conditions, fear-conditioning model has been widely used. However, simple aversive stimuli are too simplistic to understand mechanisms because most patients with psychiatric disorders are affected by social stressors. The objective of this study was to test the feasibility of a newly-designed conditioning experiment using a stimulus to cause interpersonal conflicts and examine associations between personality traits and response to that stimulus. Twenty-nine healthy individuals underwent the fear conditioning and extinction experiments in response to three types of stimuli: a simple aversive sound, disgusting pictures, and pictures of an actors’ face with unpleasant verbal messages that were designed to cause interpersonal conflicts. Conditioned response was quantified by the skin conductance response (SCR). Correlations between the SCR changes, and personality traits measured by the Zanarini Rating Scale for Borderline Personality Disorder (ZAN-BPD) and Revised NEO Personality Inventory were explored. The interpersonal conflict stimulus resulted in successful conditioning, which was subsequently extinguished, in a similar manner as the other two stimuli. Moreover, a greater degree of conditioned response to the interpersonal conflict stimulus correlated with a higher ZAN-BPD total score. Fear conditioning and extinction can be successfully achieved, using interpersonal conflicts as a stimulus. Given that conditioned fear caused by the interpersonal conflicts is likely associated with borderline personality traits, this paradigm could contribute to further understanding of underlying mechanisms of interpersonal fear implicated in borderline personality disorder.  相似文献   
1000.

Background

Despite the marked increase of diverticulosis, its risk factors have not been adequately elucidated. We therefore aim to identify significantly associated factors with diverticulosis. We also aim to investigate the present state of diverticulosis in Japan.

Methods

We reviewed the medical records from 1990 to 2010 that included the data of consecutive 62,503 asymptomatic colonoscopy examinees from the general population in Japan. Most recent 3,327 examinees were analyzed with 16 background factors.

Results

Among the 62,503 subjects (47,325 men and 15,178 women; 52.1 ± 9.2 years old), diverticulosis was detected in 11,771 subjects (18.8%; 10,023 men and 1,748 women). The incidences of diverticulosis in 1990-2000 and 2001-2010 were respectively 13.0% (3,771 of 29,071) and 23.9% (8,000 of 33,432): the latter was much higher than the former in all age groups and for both genders. Considering the anatomical locations of colorectal diverticula, left-sided ones have markedly increased with age but not significantly changed with times. Univariate analyses of the 3,327 subjects showed significant association of diverticulosis with four basic factors (age, sex, body mass index, blood pressure), three life style-related factor (smoking, drinking, severe weight increase in adulthood), and two blood test values (triglyceride, HbA1c). The multiple logistic analysis calculating standardized coefficients (β) and odds ratio (OR) demonstrated that age (β = 0.217-0.674, OR = 1.24-1.96), male gender (β = 0.185, OR = 1.20), smoking (β = 0.142-0.200, OR = 1.15-1.22), severe weight increase in adulthood (β = 0.153, OR = 1.17), HbA1c (β = 0.136, OR = 1.15), drinking (β = 0.109, OR = 1.11), and serum triglyceride (β = 0.098, OR = 1.10) showed significantly positive association with diverticulosis whereas body mass index and blood pressure did not.

Conclusions

The large-scale data of asymptomatic colonoscopy examinees from the general population from 1990 to 2010 indicated that the prevalence of diverticulosis is still increasing in Japan. Age, male gender, smoking, severe weight increase in adulthood, serum HbA1c, drinking, and serum triglyceride showed significant positive association with diverticulosis.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号