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   5762篇
  免费   642篇
  国内免费   2篇
  6406篇
  2021年   56篇
  2018年   46篇
  2017年   47篇
  2016年   81篇
  2015年   148篇
  2014年   196篇
  2013年   232篇
  2012年   264篇
  2011年   265篇
  2010年   178篇
  2009年   153篇
  2008年   256篇
  2007年   260篇
  2006年   275篇
  2005年   244篇
  2004年   278篇
  2003年   258篇
  2002年   230篇
  2001年   97篇
  2000年   69篇
  1999年   80篇
  1998年   70篇
  1997年   58篇
  1996年   67篇
  1995年   56篇
  1994年   61篇
  1993年   76篇
  1992年   83篇
  1991年   78篇
  1990年   83篇
  1989年   78篇
  1988年   62篇
  1987年   73篇
  1986年   104篇
  1985年   80篇
  1984年   68篇
  1983年   79篇
  1982年   73篇
  1981年   74篇
  1980年   61篇
  1979年   67篇
  1978年   71篇
  1977年   47篇
  1976年   76篇
  1975年   57篇
  1974年   59篇
  1973年   61篇
  1972年   54篇
  1971年   48篇
  1969年   41篇
排序方式: 共有6406条查询结果,搜索用时 0 毫秒
111.
R S Martin  T J Marrie  L Best  R K Sumarah  R Peppard 《CMAJ》1984,131(9):1085-1087
Legionella pneumophila is rarely isolated from blood cultures. Presently most cases of Legionnaires'' disease are diagnosed retrospectively from the results of indirect fluorescent antibody tests, which possess inherent disadvantages. An 81-year-old woman with a history of diabetes mellitus presented symptoms of Legionnaires'' disease. Five hours before her death 1.5 mL of blood was withdrawn from a scalp vein and seeded to a culture medium. Following incubation for 3 days L. pneumophila serotype 1 was isolated.  相似文献   
112.
The effectiveness of budesonide, a new non-halogenated glucocorticoid administered by nasal inhaler, was evaluated in a double blind comparison with placebo in patients presenting with hay fever. Patients were supplied with antihistamine tablets and eye drops for use when they considered that their symptoms were inadequately controlled by their inhaler. Patients recorded the severity of their symptoms in a daily diary card and visited their general practitioner for assessment weekly for four weeks. All nasal symptoms of hay fever were appreciably reduced in the group taking budesonide and, although their eye symptoms were more severe than in the group taking placebo, they did not use appreciably more eye drops than the latter. The placebo group used appreciably more antihistamine tablets than those in the budesonide group. No patients were withdrawn from the budesonide group because of treatment failure or unacceptable side effects. The results suggest that budesonide is an acceptable and effective treatment for the nasal symptoms of hay fever.  相似文献   
113.
Summary HeLa and L-M cells can be effectively grown directly on glass fiber filters to yield replicate cultures that allow easy analysis of biosynthetic capabilities through measurement of radioactive precursor uptake and incorporation. The glass fiber filters are superior to glass cover slips, growth in scintillation vials, and growth on Millipore filters in the ease of handling during experimental treatment and in the amount of radioactivity incorporated during the labeling period. These parameters are experimentally established and a typical application of the procedure that demonstrates the hydroxyurea inhibition of DNA synthesis is presented. This research was supported by Oklahoma Agricultural Experiment Station Project 1534. This publication is Article J-3334 of the Oklahoma Agricultural Experimental Station.  相似文献   
114.
The mechanism by which the utilization of transferrin-bound iron is linked with cellular metabolism was investigated using rabbit reticulocytes and bone marrow cells. The rate of metabolism was altered by the use of inhibitors which act at different sites in the metabolic pathway (NaF, sodium fluoroacetate, rotenone, 2,4-dinitrophenol, NaCN) and by the addition of metabolic substrates (inosine, sodium pyruvate, sodium lactate). Measurements were made of the rates of iron and transferrin uptake and, in many of the experiments, of cellular ATP and NADH concentrations. The results showed that there was a significant correlation between the rate of iron uptake and the ATP concentration of the cells, but no correlation was found with the NADH concentration. The rate of transferrin uptake was inhibited to a lesser degree than that of iron uptake, and only when the ATP concentration had fallen below that necessary to inhibit iron uptake. It is concluded that the rate of uptake of transferrin-bound iron by immmature erythroid cells is dependent on the intracellular concentration of ATP but is independent of the NADH concentration.  相似文献   
115.
A simple procedure for the measurement of submicrogram quantities of protein is described which can be used without interference from most common reagents. Protein-containing solutions are spotted on glass fiber filters, washed with trichloroacetic acid, and stained with Coomassie blue. The filters are destained, and the protein-bound colorant is eluted and measured in a spectrophotometer at 590 nm. The response is linear to 5 μg of protein per filter, and as little as 0.1 μg per filter can be accurately determined.  相似文献   
116.
The isolation of syncytium-producing mutants of herpes simplex virus type 1 (KOS strain), which cause extensive cell fusion during otherwise normal infections, has been reported previously (S. Person, R. W. Knowles, G. S. Read, S. C. Warner, and V. C. Bond, J. Virol. 17:183-190, 1976). Seven of these mutants, plus two syncytial strains obtained elsewhere, were used to compare the incorporation of labeled galactose into neutral glycolipids of mock-infected, wild-type-infected, and syncytially infected human embryonic lung cells. Five predominant cellular glycolipid species were observed, denoted GL-1 through GL-5 in order of increasing oligosaccharide chain length; for example, GL-1 and GL-2 correspond to glycolipids that contain mono- and disaccharide units, respectively. Wild-type virus infection caused an increase in galactose incorporation into GL-1 and GL-2 relative to GL-3 through GL-5. For a single labeling interval from 4 to 10 h after adsorption, syncytial infections generally resulted in a relatively greater incorporation into more complex glycolipids than did wild-type infections. One mutant, syn 20, was compared with wild-type virus throughout infection by using a series of shorter labeling pulses and appeared to delay by at least 2 h the alterations observed during wild-type infections. These alterations are apparently due to defects in synthesis, since prelabeled cellular glycolipids were not differentially degraded during mock or virus infection.  相似文献   
117.
Summary The effects of the sodium ionophore monensin on osmotic water flow across the urinary bladder of the toadBufo marinus were studied. Monensin alone did not alter osmotic water flow; however, the ionophore inhibited the hydrosmotic response to vasopressin and cyclic AMP in a dose-dependent manner. The inhibitory effects of monensin were apparent when the ionophore was added to the serosal bathing solution but not when it was added to the mucosal bathing solution. The inhibitory effect of serosal monensin required the presence of sodium in the serosal bathing solution but not the presence of calcium in the bathing solutions. Thus, it appears that intracellular sodium concentration is a regulator of the magnitude of the hydrosmotic response to vasopressin and cyclic AMP.  相似文献   
118.
Three of 16 juvenile rhesus monkeys (Macaca mulatta) and 1 rhesus of 79 adult rhesus and cynomolgus monkeys (Macaca fascicularis) were found comatose in a state of profound hypothermia after a heating failure occurred in the room in which they were housed. One juvenile monkey died shortly thereafter. The three other monkeys were revived with gradual warming and supportive therapy but later experienced separate acute clinical crises manifesting shock and died at 19, 31, and 51 days after the initial episode. Histopathologic findings of severe bone marrow depletion were observed in each of the three monkeys that died after the initial episode.  相似文献   
119.
Prosthecate bacteria comprised 0.6 to 10.5% of the bacterial community in samples from 11 pulp mill waste aeration lagoons. Because of their distinct morphology, the genera Ancalomicrobium, Caulobacter, Prosthecobacter, Prosthecomicrobium, Stella, and Hyphomicrobium or Hyphomonas could be identified and enumerated by direct microscopic examination. Monthly samples from one lagoon showed that several genera varied from undetectable to predominant among the appendaged organisms. Temperature (season), type of wood pulped, and pulping process did not significantly affect the density of prosthecate bacteria.  相似文献   
120.
The temperature dependency of the partitioning of p-alkylphenols and p-halophenols has been determined between dimyristoyl phosphatidylcholine liposomes and 0.15 M NaCl. Partition coefficients increased as a function of temperature below the endothermic phase transition temperature (Tc) of the phospholipid but decreased above this temperature. The transfer process was found to be entropy-dominated below and enthalpy-dominated above the Tc, although large negative entropy changes were observed. Regular changes in the thermodynamic functions, partition coefficients and functional group free energies occurred as a function of the alkyl chain length or size of the halogen substituent below but not above the Tc. This has tentatively been attributed to increased phenol-phospholipid interaction at the higher temperatures. The partitioning of p-fluorophenol behaved in a manner expected of fluorinated compounds, yielding relatively low partition coefficients, but it produced an additional effect of markedly lowering the Tc of dimyristoyl phosphatidylcholine. Good correlations of the partition coefficients in liposomes with those in bulk organic solvents and with molecular size of the solute have been obtained.  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