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   12445篇
  免费   637篇
  国内免费   58篇
耳鼻咽喉   117篇
儿科学   203篇
妇产科学   163篇
基础医学   1554篇
口腔科学   249篇
临床医学   808篇
内科学   2982篇
皮肤病学   299篇
神经病学   647篇
特种医学   505篇
外科学   2776篇
综合类   65篇
预防医学   386篇
眼科学   138篇
药学   744篇
中国医学   22篇
肿瘤学   1482篇
  2023年   80篇
  2022年   121篇
  2021年   219篇
  2020年   109篇
  2019年   165篇
  2018年   212篇
  2017年   195篇
  2016年   201篇
  2015年   248篇
  2014年   276篇
  2013年   335篇
  2012年   555篇
  2011年   596篇
  2010年   389篇
  2009年   306篇
  2008年   612篇
  2007年   667篇
  2006年   662篇
  2005年   721篇
  2004年   698篇
  2003年   621篇
  2002年   672篇
  2001年   389篇
  2000年   387篇
  1999年   391篇
  1998年   223篇
  1997年   163篇
  1996年   158篇
  1995年   117篇
  1994年   81篇
  1993年   113篇
  1992年   228篇
  1991年   196篇
  1990年   182篇
  1989年   179篇
  1988年   161篇
  1987年   166篇
  1986年   150篇
  1985年   161篇
  1984年   110篇
  1983年   106篇
  1982年   52篇
  1979年   82篇
  1978年   62篇
  1977年   45篇
  1974年   48篇
  1973年   49篇
  1971年   52篇
  1969年   44篇
  1968年   45篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Defensins are cationic antimicrobial peptides with a broad spectrum. Recently human beta-defensin 2 (hBD-2) has been isolated from psoriatic skin; however, its exact localization and fate have not been fully understood. We studied the distribution pattern of hBD-2 in skin tissues of psoriasis and other inflammatory skin diseases. In the upper spinous and granular layer of psoriasis vulgaris hBD-2 was present in the cytoplasm. In the horny layer the positive signals were in a basket-weave pattern, indicating possible accumulation of hBD-2 in the intercellular space. The similar pattern of hBD-2 distribution was observed in the lesions of nummular eczema and atopic dermatitis. hBD-2 was not detected in the section of normal elbow and knee skin. When isolated psoriatic scales were stained, hBD-2 was detected in a wrapping paper-like distribution pattern surrounding the corneocytes. In horny layer of psoriatic skin hBD-2 was closely associated or colocalized with elafin, which is known to be in extracellular space, as demonstrated by double staining. Western blot analysis using cultured human keratinocytes detected hBD-2 with an expected size in the conditioned medium and in the cell lysates when stimulated with 5% FCS or IL-alpha. These results indicate that hBD-2 was synthesized and remained in cytoplasm in the upper spinous and granular layer, and then secreted into intercellular space in the horny layer. This dynamic change in hBD-2 distribution in epidermis is certainly relevant to function as an innate host defense mechanism against invading micro-organisms.  相似文献   
92.
93.
Mitochondrial cytochrome b genes (cyt b) of 40 strains of Cryptococcus neoformans were partially sequenced to determine the genetic relations. With the exception of the type strain of C. neoformans var. neoformans, all strains contained introns in their sequences. Analysis of 386 bp of coding sequence from each strain under investigation revealed a total of 27 (6.99%) variable nucleotide sites and categorized isolates of C. neoformans into nine cyt b types. C. neoformans var. gattii included cyt b types I to V, and C. neoformans var. neoformans comprised types VI to IX. cyt b types were correlated with serotypes. All strains with cyt b types I, IV, and V were serotype B. All other strains except IFM 5878 (serotype B) with cyt b types II and III were serotype C. Serotype D strains had cyt b types VI and IX, and serotype A strains were cyt b type VIII. Of four serotype AD strains, one was cyt b type VII and the remaining three were type VIII. The phylogenetic tree based on deduced amino acid sequences divided the strains only into C. neoformans var. neoformans and C. neoformans var. gattii. These results indicate that cyt b sequences are effective for DNA typing as well as phylogenetic analysis of C. neoformans.  相似文献   
94.
Clostridium botulinum serotype B toxins 12S and 16S were separated by using a beta-lactose gel column at pH 6.0; toxin 12S passed through the column, whereas toxin 16S bound to the column and eluted with lactose. The fully activated neurotoxin was obtained by applying the trypsin-treated 16S toxin on the same column at pH 8.0; the neurotoxin passed through the column, whereas remaining nontoxic components bound to the column. The toxicity of this purified fully activated neurotoxin was retained for a long period by addition of albumin in the preparation.  相似文献   
95.
Synovial sarcoma, which has a wide spectrum of biologic behavior, warrants accurate grading to assess the patient's prognosis. We studied the clinicopathologic and immunohistochemical features of 44 cases of synovial sarcoma in patients treated primarily or secondarily at the National Cancer Center, Tokyo, to identify independent prognostic factors. There were local recurrences in 16 patients (36%), and 25 (57%) developed metastases, primarily to the lungs. The estimated cumulative 5-year and 10-year survival rates were 68% and 41%, respectively. Variables associated with an adverse outcome included tumor size > 6.7 cm; initial treatment outside the National Cancer Center; poorly differentiated subtype; high nuclear atypia; mitosis count > 27/10 high-power fields; tumor necrosis; absence of stromal calcification; nuclear expression of beta-catenin, which was found in 25 cases (57%); Ki-67 (MIB-1) index > 27%; and histologic grade 3. Nuclear accumulation of beta-catenin as a cell-signaling event may play an important role in the progression of synovial sarcoma and therefore might be predictive of short survival. However, multivariate analysis clearly showed that only histologic grade, as defined by using categorized variables for the MIB-1 index and tumor necrosis, was an independent prognostic factor. Most variables were correlated with lung metastasis and histologic grade. High-grade synovial sarcoma assessed by a histologic grading system based on the proliferative activity of the neoplastic cells can be viewed as high risk with the patients most likely to die of disease within 10 years after surgery and in need of improved chemotherapy. HUM PATHOL 32:257-263.  相似文献   
96.
Severe inflammatory responses after major surgeries, trauma, and infection develop multiple organ dysfunction. In the mechanisms of the pathogenesis of these responses, activated neutrophils are thought to be important in terms of their ability to produce various kinds of proteinases, which can degrade various proteins constructing human tissues. Among their proteinases, neutrophil elastase is the strongest serine proteinase secreted from activated neutrophils. Thus, we examined in this study the inhibitory effect and therapeutic efficacy of newly produced recombinant human Kunitz-type proteinase inhibitor (R-020), which coded the second domain of human urinary trypsin inhibitor. R-020 was effective in significantly improving the survival rate after induction of the rat lethal peritonitis model (cecal ligation and punctureinduced septic shock model). We suggest that various serine proteinases are implicated in the pathogenesis of neutrophil-related multiple organ failure and that recombinant human Kunitz-type proteinase inhibitor might be effective in the treatment of these kinds of organ dysfunction.  相似文献   
97.
Saposin C is a biological activator of acid beta-glucosidase (GCase), the lysosomal hydrolase with activity towards glucosylceramide (GC). In addition, saposin C possesses a functional domain that determines the in vitro and ex vivo neuritogenic effects of prosaposin, the precursor of saposins A, B, C, and D. The domains for enzymatic activation and neuritogenic function segregate in vitro, respectively, to the carboxyl- and amino-terminal halves of human and mouse saposin C. A chimeric mouse saposin C(1-8)B(8-28)C(30-80) was created to obliterate the neuritogenic region by substituting amino acids 9-29 of saposin C with amino acids 8-28 of saposin B. This saposin showed normal in vitro enzymatic activation effects toward GCase, but no neuritogenic activity. An altered prosaposin was made to contain the chimeric saposin C region. Expression of this altered or wild-type prosaposin was driven by the PGK-1 promoter as a transgene in prosaposin knock-out mice. In cultured fibroblasts from such mice, expressed saposins localized to the lysosomal compartments. Metabolic lipid labeling using L-[3-(14)C]serine showed retention or clearance of GC in prosaposin deficient or transgene reconstituted cells, respectively. In addition, sulfatide catabolism, that requires saposin B and arylsulfatase, was also normalized in prosaposin KO cells reconstituted with the transgenes. These data show that the transgenic prosaposins were expressed and processed to functional saposins in fibroblasts. These results also show that the enzymatic activation domain is located at carboxyl-terminal half of saposin C and functions only in the context of the general saposin structure.  相似文献   
98.
This report presents a case of neural fibrolipoma arising from the superficial peroneal nerve in the ankle. A 28-year-old woman was referred with a soft tissue mass in the anterior aspect of the right ankle, which had been gradually enlarging for the past 10 years. Magnetic resonance imaging showed a mass lesion, measuring approximately 8 x 3 x 2 cm, with high to partially low signal intensity on both T1- and T2-weighted images. A band of low signal intensity within the lesion, which is indicative of coexistence with the tumor and the superficial peroneal nerve, could be detected on both T1- and T2-weighted images. The patient underwent an excisional biopsy. The specimen microscopically consisted of nerve bundles and fibro-fatty proliferation with abundant collagen fibers. Immunoreactivity for CD34 antigen antibody was detected in fibrous spindle cells. This is the first report to present an immunohistochemical profile of neural fibrolipoma. Neural fibrolipoma should be considered as a differential diagnosis when a lipomatous lesion is encountered in the foot or ankle as well as in the upper extremities.  相似文献   
99.
There are regional variations of sex chromosome morphologies in the Japanese wrinkled frog, Rana rugosa (2n = 26): heterogametic ZZ/ZW-type and XX/XY-type sex chromosomes, and two different types of homomorphic sex chromosomes. To search for homology between the ZW and XY sex chromosomes and the chromosome rearrangements that have occurred during sex chromosomal differentiation in R. rugosa, we performed chromosome mapping of sexual differentiation genes for R. rugosa by FISH. Three genes, AR, SF-1/Ad4BP and Sox3, were localized to both the ZW and XY chromosomes, and their locations were all different between the Z and W and between the X and Y. AR and SF-1/Ad4BP were located on the short arms of the W and X and the long arms of Z and Y, and Sox3 was mapped to the different locations on the long arms between the Z and W and between the X and Y, probably as a result of multiple rearrangements that occurred during the process of sex chromosome differentiation. However, the chromosomal locations of three genes were almost consistent between the Z and Y and between the W and X, indicating that the Z and Y chromosomes and the W and X chromosomes were respectively derived from the same origins. Dmrt1, which is located on avian sex chromosomes, was localized to autosomes in R. rugosa with both the ZW and XY sex chromosomes, suggesting that Dmrt1 might not be related to sex determination in this species.  相似文献   
100.
Skeletal muscle is composed of several different types of myofiber: slow oxidative (SO), fast glycolytic oxidative and fast glycolytic. However, the classification is usually determined by myosin heavy chain typing rather than by metabolic index. In this study, the oxidative metabolic index was investigated as a possible method of myofiber typing. Myoglobin, which is involved in oxygen transport and storage in myofibers, and mitochondria, which are the central organelles for oxidative metabolism, were studied. High levels of myoglobin and mitochondria are believed to exist in SO fibers, but the current study showed that they are considerably richer in some fast type fibers. As myofiber typing using the oxidative metabolic index is important physiologically, an attempt was made to find a simple method for this purpose. Some mitochondrial proteins have been observed to auto-fluoresce but until now this effect was too faint to detect easily. Owing to the recent advances in cooling charge-coupled device technology, such auto-fluorescence can now be used for myofiber typing, and the simple and rapid method for doing so is reported here.  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