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   6341篇
  免费   241篇
  国内免费   16篇
耳鼻咽喉   50篇
儿科学   150篇
妇产科学   240篇
基础医学   1398篇
口腔科学   114篇
临床医学   465篇
内科学   1381篇
皮肤病学   111篇
神经病学   490篇
特种医学   129篇
外科学   442篇
综合类   23篇
一般理论   2篇
预防医学   489篇
眼科学   117篇
药学   711篇
中国医学   22篇
肿瘤学   264篇
  2023年   37篇
  2022年   62篇
  2021年   104篇
  2020年   66篇
  2019年   89篇
  2018年   138篇
  2017年   108篇
  2016年   135篇
  2015年   155篇
  2014年   182篇
  2013年   277篇
  2012年   431篇
  2011年   437篇
  2010年   224篇
  2009年   176篇
  2008年   256篇
  2007年   350篇
  2006年   339篇
  2005年   262篇
  2004年   298篇
  2003年   265篇
  2002年   261篇
  2001年   119篇
  2000年   141篇
  1999年   128篇
  1998年   44篇
  1992年   78篇
  1991年   50篇
  1990年   77篇
  1989年   72篇
  1988年   58篇
  1987年   45篇
  1986年   70篇
  1985年   52篇
  1984年   52篇
  1983年   33篇
  1982年   29篇
  1979年   57篇
  1978年   59篇
  1977年   43篇
  1976年   39篇
  1975年   60篇
  1974年   50篇
  1973年   49篇
  1972年   52篇
  1971年   55篇
  1970年   52篇
  1969年   47篇
  1968年   32篇
  1967年   43篇
排序方式: 共有6598条查询结果,搜索用时 171 毫秒
41.

Background

Increased body fat may be associated with an increased risk of developing an underlying pro-inflammatory state, thus leading to greater risk of developing certain chronic conditions. Immunoglobulin G has the ability to exert both anti- and pro-inflammatory effects, and the N-glycosylation of the fragment crystallisable portion is involved in mediating this process. Body mass index, a rudimentary yet gold standard indication for body fat, has been shown to be associated with agalactosylated immunoglobulin G N-glycans.

Aim

We aimed to determine the association between increased body fat and the immunoglobulin G glycosylation features, comparing body mass index to other measures of body fat distribution.

Methods

We investigated a sample of 637 community-based 45–69?year olds, with mixed phenotypes, residing in Busselton, Western Australia. Body mass index and the waist-to-hip and waist-to-height ratios were calculated using anthropometry, while dual-energy x-ray absorptiometry was performed to gain an accurate measure of total and area specific body fat. Serum immunoglobulin GN-glycans were analysed by ultra-performance liquid chromatography.

Results

Twenty-two N-glycan peaks were found to be associated with at least one of the fat measures. While the previous association of body mass index to agalactosylated immunoglobulin G was replicated, measures of central adiposity explained the most variation in the immunoglobulin G glycome.

Conclusion

Central adiposity is associated with an increased pro-inflammatory fraction of immunoglobulin G, suggesting that the android/gynoid ratio or waist-to-height ratio instead be considered when controlling for adiposity in immunoglobulin G glycome biomarker studies.  相似文献   
42.
A number of molecular genetic studies have investigated if serotonin (5-HT) receptor subtypes are involved in the pathogenesis of depression, suicidal behavior, aggression, and impulsive behavior. Existence of many receptor subtypes for a single transmitter permits a great diversity of signaling raising the possibility that they may serve as genetic markers for suicidal behavior. Most previous studies of suicide have analyzed polymorphisms of the receptors 5-HT1A, 5-HT1B, 5-HT2A, fewer have examined 5-HT1F. We report a study of possible association between the polymorphisms in the 5-HT receptor genes (1A, 1B, 1F, and 2A) and suicidal behavior on a sample of 226 suicide victims and 225 healthy control subjects. No significant differences in genotype frequency distributions between the suicide victims and healthy control subjects were observed for four polymorphisms; three were not polymorphic. A single polymorphism, C-1420T in gene 5-HT2A, showed a slight association with suicide (chi2= 4.94, df = 2, P = 0.067), but the correlation was not statistically significant. None of the tested genetic variants of serotonin receptors appears to be associated with suicidal behavior in the Slovenian population which has a relatively high suicide rate.  相似文献   
43.
Although Smith-Lemli-Opitz Syndrome (SLOS), a genetic condition of impaired cholesterol biosynthesis, is associated with autism [Tierney et al., 2001; Am J Med Genet 98:191-200.], the incidence of SLOS and other sterol disorders among individuals with autism spectrum disorders (ASD) is unknown. This study investigated (1) the incidence of biochemically diagnosed SLOS in blood samples from a cohort of subjects with ASD from families in which more than one individual had ASD and (2) the type and incidence of other sterol disorders in the same group. Using gas chromatography/mass spectrometry, cholesterol, and its precursor sterols were quantified in 100 samples from subjects with ASD obtained from the Autism Genetic Resource Exchange (AGRE) specimen repository. Although no sample had sterol levels consistent with SLOS, 19 samples had total cholesterol levels lower than 100 mg/dl, which is below the 5th centile for children over age 2 years. These findings suggest that, in addition to SLOS, there may be other disorders of sterol metabolism or homeostasis associated with ASD.  相似文献   
44.
Summary Translation of poliovirus RNA is initiated by entry of ribosomes into the nucleotide sequence (internal ribosomal entry site; IRES) within the 5-untranslated region (5-UTR). Efficiency of this translation initiation in rabbit reticulocyte lysates (RRL) was very low and was greatly enhanced by addition of the ribosomal salt-wash fraction (RSW) prepared from HeLa cells. This stimulating activity in the RSW was partially purified by gel-filtration column chromatography and its molecular weight was estimated to be higher than 240 000. Several proteins that bind specifically to the poliovirus IRES were detected in the active fraction. Among those, a 57 kDa protein, recognized by antibodies against polypyrimidide tract-binding protein (PTB), was found. In addition, La protein (52 kDa) which is a human antigen recognized by antibodies from patients with autoimmune disorders was also detected. Further purification on a hydroxylapatite column resulted in considerable loss of the stimulatory activity, accompanied by a reduction of the apparent molecular weight of active component(s). These results suggest that fully active HeLa cell stimulatory factors for the translation initiation on poliovirus RNA function in RRL as a large complex consisted of several components including PTB and La protein.  相似文献   
45.
46.
The development of the Monte Carlo code SHIELD-HIT (heavy ion transport) for the simulation of the transport of protons and heavier ions in tissue-like media is described. The code SHIELD-HIT, a spin-off of SHIELD (available as RSICC CCC-667), extends the transport of hadron cascades from standard targets to that of ions in arbitrary tissue-like materials, taking into account ionization energy-loss straggling and multiple Coulomb scattering effects. The consistency of the results obtained with SHIELD-HIT has been verified against experimental data and other existing Monte Carlo codes (PTRAN, PETRA), as well as with deterministic models for ion transport, comparing depth distributions of energy deposition by protons, 12C and 20Ne ions impinging on water. The SHIELD-HIT code yields distributions consistent with a proper treatment of nuclear inelastic collisions. Energy depositions up to and well beyond the Bragg peak due to nuclear fragmentations are well predicted. Satisfactory agreement is also found with experimental determinations of the number of fragments of a given type, as a function of depth in water, produced by 12C and 14N ions of 670 MeV u(-1), although less favourable agreement is observed for heavier projectiles such as 16O ions of the same energy. The calculated neutron spectra differential in energy and angle produced in a mimic of a Martian rock by irradiation with 12C ions of 290 MeV u(-1) also shows good agreement with experimental data. It is concluded that a careful analysis of stopping power data for different tissues is necessary for radiation therapy applications, since an incorrect estimation of the position of the Bragg peak might lead to a significant deviation from the prescribed dose in small target volumes. The results presented in this study indicate the usefulness of the SHIELD-HIT code for Monte Carlo simulations in the field of light ion radiation therapy.  相似文献   
47.
48.
The high temperature (up to 220°C.) polymerization of 3,3-bis(chloromethyl)oxetane catalyzed by i-Bu3Al was investigated. The conversion-time curves are of the autocatalytic type and the molecular weight increases lineary with conversion up to the point at which for lower temperatures, e.g. 60–80°C., the whole polymer becomes insoluble. An alternative explanation of this phenomenon is proposed; the formation of insoluble product is related to the entanglement of macromolecules of very high molecular weight and or macrocycle formation in the degradative chain transfer to polymer. The phenomenon of insoluble products formation was never observed at higher temperatures (> 150°C.). The dependence of molecular weight on catalyst and impurity concentrations as well as on the polymerization temperature was investigated. It was shown that the high molecular weight product (\documentclass{article}\pagestyle{empty}\begin{document}$\overline {DP}$\end{document} = 1000–1500) can be produced at 180–220°C. even at rather high impurity level.  相似文献   
49.
Keratin 19 and nuclear reactivity to an endogenous lectin, galectin-1, represent a potential marker of epidermal stem cells. We detected expression of keratin 19 and nuclear binding sites for galectin-1 in adult cells migrating from the hair follicle, where cells expressing keratin 19 are located in the bulge region. The results were compared with the expression of both markers in cells adhering from suspension prepared from the interfollicular epidermis without keratin-19-positive cells and with nuclear binding sites for galectin-1. The results were compared with data from basal cell carcinomas. All cells were analyzed concerning size, as it is known that cell diameter influences the clonogenic potential of keratinocytes. The major result of this study is the observation of transient expression of keratin 19 and nuclear galectin-1 binding sites in originally negative interfollicular epidermal cells induced by adhesion. These cells were very small in size, similar to basal cells of the interfollicular epidermis or the bulge region of the hair follicle. The influence of the suspension regimen on beta1-integrin expression, cell diameter and growth was also monitored. A population of cells highly positive for beta1 integrin of the same diameter as keratin-19-positive cells insensitive to induction of terminal differentiation by lack of anchorage was characterized. Cells of the same size were also observed in the keratin-19-positive cells of basal cell carcinomas. In conclusion, the expression of poor levels of differentiation induced by cell adhesion is transient. Also, keratin 19 expression should not be exclusively regarded as a marker of stem cell activity.  相似文献   
50.
A total of 28 domestic ducks were divided into seven groups of four ducks. Six groups were inoculated per os with 10(1), 10(2), 10(3), 10(4), 10(5) and 10(5.7) oocysts Toxoplasma gondii oocysts (K21 strain, which is avirulent for mice), and the remaining group was used as a control. Antibodies to T. gondii were detected in all ducks by the indirect fluorescence antibody test first on day 7 post-inoculation (p.i.). Antibody titres were found in the range of 1:20 to 1:640 depending on the infectious dose of the oocysts. From day 14 p.i. antibody titres increased to 1:80 to 1:20 480. Between days 14 and 28 p.i. (end of the experiment), antibody titres decreased in 14 ducks, remained the same in seven ducks, and continued to increase in three ducks. Bioassay in mice revealed T. gondii in the breast and leg muscles and the heart (100%, n=47), brain (91%, n=22), liver (54%, n=13) and stomach (46%, n=24). The infected ducks showed no clinical signs; however, the results of bioassay indicate that, compared with some gallinaceous birds, domestic ducks were relatively susceptible to T. gondii infection.  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