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   232篇
  免费   14篇
  国内免费   6篇
儿科学   5篇
妇产科学   32篇
基础医学   32篇
口腔科学   8篇
临床医学   36篇
内科学   25篇
神经病学   23篇
特种医学   11篇
外科学   38篇
综合类   1篇
预防医学   23篇
眼科学   1篇
药学   13篇
肿瘤学   4篇
  2023年   2篇
  2021年   7篇
  2020年   4篇
  2019年   3篇
  2018年   1篇
  2017年   11篇
  2016年   5篇
  2015年   3篇
  2014年   5篇
  2013年   3篇
  2012年   13篇
  2011年   18篇
  2010年   4篇
  2009年   5篇
  2008年   11篇
  2007年   4篇
  2006年   10篇
  2005年   12篇
  2004年   8篇
  2003年   7篇
  2002年   9篇
  2001年   12篇
  2000年   13篇
  1999年   8篇
  1998年   5篇
  1997年   4篇
  1996年   3篇
  1994年   4篇
  1993年   3篇
  1992年   5篇
  1991年   4篇
  1990年   10篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1975年   2篇
  1974年   1篇
  1973年   2篇
  1972年   2篇
  1968年   2篇
  1966年   2篇
排序方式: 共有252条查询结果,搜索用时 15 毫秒
1.
Viral culture isolation has been widely accepted as the "gold standard" for laboratory confirmation of viral infection; however, it requires ultralow temperature specimen storage. Storage of specimens in ethanol at room temperature could expand our ability to conduct active surveillance and retrospective screenings of viruses with rapid and inexpensive real-time PCR tests, including isolates from remote regions where freezing specimens for culture is not feasible. Molecular methods allow for rapid identification of viral pathogens without the need to maintain viability. We hypothesized that ethanol, while inactivating viruses, can preserve DNA and RNA for PCR-based methods. To evaluate the use of ethanol-stored specimens for augmenting surveillance for detection of influenza viruses A and B and adenoviruses (AdV), paired nasal swab specimens were collected from 384 recruits with febrile respiratory illness at Fort Jackson, S.C., in a 2-year study. One swab was stored at ambient temperature in 100% ethanol for up to 6 months, and the other swab was stored at -70 degrees C in viral medium. For viral detection, frozen specimens were cultured for a variety of respiratory viruses, and ethanol-fixed specimens were tested with TaqMan (TM) probe and LightCycler SYBR green (SG) melting curve assays with at least two different PCR targets for each virus. The sensitivities of the TM and SG assays on specimens stored in ethanol for 1 month were 75% and 58% for influenza A, 89% and 67% for influenza B, and 93 to 98% and 57% for AdV, respectively. Lower specificities of the real-time assays corresponded to the increased detection of PCR-positive but culture-negative specimens. Influenza virus RNA was detected as well or better after 6 months of storage in ethanol.  相似文献   
2.
This paper describes a GC-MS method (SIM mode) for the analysis of perfluorooctyl bromide (perflubron, I) in rat blood. The chromatographic separation was performed by injection in the split mode using a CP-select 624 CB capillary column. Following destruction of the emulsion by addition of ethanol, the analytical procedure involves a liquid-liquid extraction with 1,1,2-trichlorotrifluoroethane. The bis(F-butyl)ethene (II) was used as internal standard. Observed retention times were 3.22 min for I and 2.32 min for II. Two calibration curves were used; linear detection responses were obtained for concentrations ranging from 0.009 to 0.9 mg/ml and from 0.9 to 13.5 mg/ml. The extraction efficiency averaged 50% for I and 93% for II. Precision ranged from 0.7 to 14%, and accuracy was between 91 and 109%. The limit of quantification was 9 microg/ml. The method validation results indicate that the performance characteristics of the method fulfilled the requirements for assay method for use in pharmacokinetic studies.  相似文献   
3.
Verbal recall and recognition were examined in Huntington's disease (HD) and Alzheimer's disease (AD) patients. Subgroups of HD and AD patients were matched for overall severity of dementia. Subjects were administered the Hopkins Verbal Learning Test, a list-learning task with three free-recall trials followed immediately by one yes/no recognition trial with semantically related and unrelated distractors. The matched AD and HD groups did not differ in the number of words recalled, although the HD patients showed slightly greater improvement over trials. Recognition performance was evaluated with measures of accuracy and response bias that are independent of each other. The matched groups did not differ in overall recognition accuracy, but the AD patients tended to have a more liberal ("yea-saying") response bias than did the HD patients. In addition, only the AD patients were differentially enticed to false-positive responding by semantically related distractors. The results suggest that the rule for making decisions when uncertain, rather than memory strength per se, distinguishes the recognition memory performance of AD and HD patients.  相似文献   
4.
5.
6.
Alveolar bone quality is considered to be an important prognostic factor in dental implant stability. Although numerous methods have been described, no technique allows for reliable diagnostics. The purpose of this study was to determine if strain measurements on the shaft of a contra angle handpiece during implant bed preparation could be used for the determination of bone quality. Experiments in polyurethane foam and human cadaver bone were conducted to investigate whether strain measurements could be correlated with other diagnostic parameters, such as the surgeon's tactile sensation during drilling, implant insertion torque, implant stability, elastic modulus of bone and bone quality as assessed radiographically. Tests were also performed to determine if strain measurements could be used to distinguish various types of bone. As axial feed and contact pressure during the drilling process could not be standardized under simulated clinical conditions, substantial deviations in the time needed to complete the drilling occurred. Under controlled circumstances using polyurethane foam, this problem could be addressed by a normalization procedure, but great variations occurred in human cadaver bone. As bone quality could not be reliably determined, especially when a cortical layer was present, strain measurements on a contra angle handpiece appears to be inappropriate for this purpose.  相似文献   
7.
The global yield of bananas—one of the most important food crops—is severely hampered by parasites, such as nematodes, which cause yield losses up to 75%. Plant–nematode interactions of two banana cultivars differing in susceptibility to Radopholus similis were investigated by combining the conventional and spatially resolved analytical techniques 1H NMR spectroscopy, matrix-free UV-laser desorption/ionization mass spectrometric imaging, and Raman microspectroscopy. This innovative combination of analytical techniques was applied to isolate, identify, and locate the banana-specific type of phytoalexins, phenylphenalenones, in the R. similis-caused lesions of the plants. The striking antinematode activity of the phenylphenalenone anigorufone, its ingestion by the nematode, and its subsequent localization in lipid droplets within the nematode is reported. The importance of varying local concentrations of these specialized metabolites in infected plant tissues, their involvement in the plant’s defense system, and derived strategies for improving banana resistance are highlighted.Bananas and plantains (Musa spp.) are among the world’s most important food and cash crops, with a global production of about 138 million tons in 2010. These crops are part of a well-balanced human diet and are a major food staple for more than 400 million people in the tropics (1, 2). About 82% of the world’s banana production is consumed locally, particularly in India, China, and many African countries (Table S1) (1, 2). Export of bananas to the northern hemisphere represents an important source of employment in countries such as Costa Rica, Ecuador, Colombia, and the Philippines (Table S2) (1, 2). Banana yields are severely hampered by fungi, insects, and plant-parasitic nematodes. The burrowing nematode, Radopholus similis (Cobb, 1893) Thorne, 1949, is the key nematode pathogen, causing yield losses up to 75% (3). R. similis is found in all major banana-producing regions of the world; its best-known hosts are bananas, black pepper, Citrus spp. (4), and coffee (5). R. similis causes extensive root lesions that can lead to toppling of banana plants (6).Plant-parasitic nematodes have been effectively managed through the use of nematicides. However, their high toxicity has adverse effects on humans and their toxic residues are known to accumulate through nontarget organisms in the food chain (7). After the withdrawal of many effective nematicides, such as methyl bromide, from the market (8), organophosphate and carbamate nematicides are still intensively applied to banana and therefore continue to threaten the health of agricultural workers and the environment (9). Although several biological control approaches, including the application of both single and multiple control organisms—such as Fusarium oxysporum, Paecilomyces lilacinus, Trichoderma atroviride isolates, and Bacillus firmus—have proved promising under greenhouse conditions, the control they confer to banana plants most probably does not protect plants for more than one cycle in the field, and most of these organisms have yet to be tested under field conditions (10).The in-depth investigation of the plant–nematode interactions at the cellular and molecular level could lead to the development of more rational and efficient control strategies (11). The production of toxic, herbivore-deterrent or -repellent secondary metabolites, which is typical for many plant defense systems, is particularly interesting in this context. Musa cultivars resistant to R. similis have been identified, especially the cultivar Yangambi km5 (Ykm5) (12). Histochemical and ultrastructural investigations of lesions caused by R. similis in Ykm5 revealed the accumulation of phenolic compounds in response to infection (13). Unfortunately, many of these studies were based solely on histochemical staining methods and did not identify the chemical structures of nematicidal secondary metabolites (7, 14, 15). Initial phytochemical analyses of R. similis-infected roots of the Musa cultivar Pisang sipulu identified the phenylphenalenone anigorufone (1) as a phytoalexin produced in response to nematode damage and confirmed earlier suggestions of the significant role of phytoalexins in the plant defense system (16). Phenylphenalenones are a group of special phenylpropanoid-derived natural products (17), which are known as Musaceae phytoalexins (18). The activity of phenylalanine ammonia lyase (EC 4.3.15), the entry-point enzyme of the phenylpropanoid pathway, is correlated to the biosynthesis of specific phenylpropanoids involved in defense and was substantially induced in nematode infected roots of Ykm5 (19). Phenylphenalenone-related compounds show biological activity against bacteria, fungi, algae, and diatoms (18, 2022). The formation of these compounds has been elicited in banana leaves by Mycosphaerella fijiensis (Black Sigatoka leaf streak disease), in the fruit peels by Colletotrichum musae (anthracnose disease), and in roots and rhizomes by F. oxysporum f. sp. cubense (Panama disease) and R. similis (16, 18, 21, 23).  相似文献   
8.
There are reported preliminary results of a pilot-study in the postoperative adjuvant treatment of cervical carcinoma with involvement of the iliac lymph nodes. It was done a prospective randomized study. There were 3 groups of treatment: adjuvant chemotherapy with a combination of Cisplatin and 5-Fluorouracil over 6 cycles; adjuvant chemotherapy like in the first group over 3 cycles plus Telecobalt-irradiation till the doses of 50 Gy in the small pelvis; and postoperative irradiation with Telecobalt till the doses of 50 Gy in the small pelvis. The fate of 41 patients could be evaluated. There were no statistical differences between the 3 groups in age, histology, staging and follow-up. Also the survival rate and the rate of the disease-free time didn't show a significant difference, but it seems, that the chemotherapy with Cisplatin and 5-Fluorouracil could be able to improve the poor prognosis of the cervical carcinoma with metastases.  相似文献   
9.
According to our experiences the incorporation of 3H-thymidine in ovarian cancer cells determined by autoradiography represents a method of additional tumour characterization. The in-vitro-tests allow roughly hints about the efficiency of an intended therapy in 49 patients suffering from ovarian cancer. High risk patients may be excluded from a chemotherapy, if the incorporation of thymidine is low. For this decision we also evaluate the results of oncobiogram and clinical parameters. The 3H-thymidine incorporation enables to elect an individual kind of therapy for any patient with regard to success and duration of treatment.  相似文献   
10.
Cisplatinum (DDP) is a cell cycle-independent drug used to prolong the survival time in ovarian cancer patients operated palliatively. After six therapeutic cycles of 100 mg of cisplatinum (Platidiam, Lachema, Brno) per square meter of body surface each changes in the sensation of hearing like tinnitus without any limitation of the faculty of hearing felt individually have been reported in four out of twelve ovary cancer patients. A high frequency loss of more than 4,000 Hz could be detected by threshold audiometry in three out of these twelve patients.  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