全文获取类型
收费全文 | 125940篇 |
免费 | 10887篇 |
国内免费 | 8146篇 |
专业分类
耳鼻咽喉 | 1019篇 |
儿科学 | 1561篇 |
妇产科学 | 2322篇 |
基础医学 | 14802篇 |
口腔科学 | 2059篇 |
临床医学 | 16404篇 |
内科学 | 20669篇 |
皮肤病学 | 1448篇 |
神经病学 | 6874篇 |
特种医学 | 4296篇 |
外国民族医学 | 70篇 |
外科学 | 13092篇 |
综合类 | 18905篇 |
现状与发展 | 24篇 |
一般理论 | 5篇 |
预防医学 | 7809篇 |
眼科学 | 3651篇 |
药学 | 12774篇 |
115篇 | |
中国医学 | 6038篇 |
肿瘤学 | 11036篇 |
出版年
2024年 | 345篇 |
2023年 | 1822篇 |
2022年 | 4658篇 |
2021年 | 5862篇 |
2020年 | 4222篇 |
2019年 | 4061篇 |
2018年 | 4128篇 |
2017年 | 3689篇 |
2016年 | 3460篇 |
2015年 | 5213篇 |
2014年 | 6533篇 |
2013年 | 6090篇 |
2012年 | 8900篇 |
2011年 | 9758篇 |
2010年 | 5945篇 |
2009年 | 4733篇 |
2008年 | 6506篇 |
2007年 | 6496篇 |
2006年 | 6536篇 |
2005年 | 6478篇 |
2004年 | 4458篇 |
2003年 | 4211篇 |
2002年 | 3559篇 |
2001年 | 3223篇 |
2000年 | 3309篇 |
1999年 | 3450篇 |
1998年 | 2243篇 |
1997年 | 2168篇 |
1996年 | 1564篇 |
1995年 | 1457篇 |
1994年 | 1266篇 |
1993年 | 819篇 |
1992年 | 1227篇 |
1991年 | 1075篇 |
1990年 | 931篇 |
1989年 | 823篇 |
1988年 | 712篇 |
1987年 | 668篇 |
1986年 | 508篇 |
1985年 | 463篇 |
1984年 | 249篇 |
1983年 | 178篇 |
1982年 | 118篇 |
1981年 | 116篇 |
1980年 | 76篇 |
1979年 | 120篇 |
1978年 | 59篇 |
1976年 | 52篇 |
1975年 | 55篇 |
1974年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
在建立小鼠胸腺基质细胞株时发现小鼠胸腺基质细胞株MTSCB和MTSCC自发产生多核细胞及单核巨细胞,对上述细胞进行了非特异性酯酶(NSE)、酸性磷酸酶(AcP)和琥珀酸脱氢酶(SDH)反应,多核细胞及单核巨细胞的NSE、AcP和SDH活性均强于单核小细胞。在MTSCB中多核细胞的百分数为1.1%;MTSCC中多核细胞为0.6%,实验中对一核细胞和多核细胞出现的百分数与Poisson分布的理论频率进 相似文献
962.
963.
Sequences at the 3'-ends of both positive and negative strands of Hepatitis C virus (HCV) RNA harbor cis-acting elements required for RNA replication. However, little is known about the properties of the negative RNA strand as a template for the synthesis of positive RNA strand. In this study, a purified recombinant HCV RNA-dependent RNA polymerase (RdRp) was used to investigate the synthesis of positive RNA strand using the 3'-terminal region of negative RNA strand ((-)3'T RNA) as template. A mutagenesis analysis was performed to evaluate the role of the 3'-proximal stem-loop and the first 3'-cytidylate (3'C) of the negative RNA strand in the synthesis of the positive RNA strand. A negative RNA strand of wild type (wt) HCV as template was able to direct the synthesis of a full-length positive RNA strand. Deletion of the 3'-proximal stem-loop resulted in an approximately 90% decrease in RNA synthesis. Disruption of the 3'-proximal stem-loop structure by nucleotide substitutions led to a 70-80% decrease in RNA synthesis. However, the restoration of the stem-loop by compensatory mutations in the stem region restored also the RNA synthesis. Likewise, the deletion or substitution of the first 3'C by guanylate (G) led to a 90% decrease in the RNA synthesis; while the substitution by adenylate (A) or uridylate (U) resulted in a 60-80% decrease in the RNA synthesis only. These findings demonstrate that the 3'-proximal stem-loop and the first 3'C of the negative RNA strand of HCV are two cis-acting elements involved in the synthesis of the positive RNA strand. 相似文献
964.
Wu YG Widjaja SL Huang CY Li W Nixon PF Duggleby RG 《Molecular genetics and metabolism》2001,72(3):269-272
One cause of congenital lactic acidosis is a mutation in the E1 alpha-subunit of the pyruvate dehydrogenase multienzyme complex. Little is known about the consequences of these mutations at the enzymatic level. Here we study the A199T mutation by expressing the protein in Escherichia coli. The specific activity is 25% of normal and the K(m) for pyruvate is elevated by 10-fold. Inhibitors of lactate dehydrogenase might be a useful therapy for patients with such mutations. 相似文献
965.
966.
Wu AH Holtman V Apple FS Ricchiuti V DiBello PM Jacobsen D 《Annals of clinical and laboratory science》2000,30(2):185-190
A fully automated immunoassay for total plasma homocysteine assay was evaluated at four centers. To measure total homocysteine, oxidized forms of homocysteine in serum and plasma were reduced by dithiothreitol and assayed by a competitive fluorescence polarization technique. The assay had within-run precision from 0.9 to 3.0% and total precision from 2.8 to 4.1% for control materials with homocysteine concentrations of approximately 7, 12.5, and 25 micromol/L, a sensitivity of 0.35 micromol/L, good parallelism upon dilution, and analytical recovery ranging from 97.4 to 103.8%. The immunoassay correlated with four different HPLC assays for homocysteine, yielding a slope of 0.98, an intercept of -0.19 micromol/L, and a correlation coefficient of 0.966 for 440 paired samples. The reference range, determined with plasma samples from 609 males and 600 females, yielded a mean of 9.17+/-2.86 micromol/L, with a central 95% range of 4.78-15.43 micromol/L. The immunoassay is a suitable alternative to HPLC and may be useful in screening persons with high risk of coronary artery disease. 相似文献
967.
In order to clarify morphology and function(s) of the terminal nerve, gross examinations of the nerve were carried out in 9 species of selachians. The terminal ganglion was observed light- and electron-microscopically. FMRF-amide immunoreactivity of the terminal nerve was also examined in some species. The results were as follows: 1) The terminal nerve was divided into peripheral and central branches by interposed ganglion(s). Macroscopically, the peripheral branch appeared from an area between the nasal sac and the olfactory bulb. The central branch entered the telencephalon from either the rostral, dorsal, or ventral surface. The position seemed to differ from species to species. 2) The terminal nerve showed great species differences and individual variations in the macroscopic morphology, such as number and course of the peripheral branch, position, size and number of ganglia, and telencephalic areas where the central branch entered. Even in the same individual, there was a difference in left and right sides. 3) According to general histology, the ganglion was encapsulated and had no direct connection with the telencephalon through the capsule, even when the ganglion was situated on the telencephalon. The Bodian preparations showed that most ganglion cells were unipolar, and a few were bipolar or pseudounipolar. 4) All ganglion cells and the processes were FMRF-amide immunoreactive. Immunoreactive fibers of the central branch terminated in the septal and preoptic areas. FMRF-amide immunoreactive cells were also found in the olfactory nerves or the septal area of the telencephalon in some species. These neurons were thought to be ectopic ganglion cells. 5) Neuronal somata and the axons in the ganglion contained large dense cored vesicles.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
968.
The number of sodium pump sites on erythrocytes was measured on 1,847 individuals in 80 Utah kindreds ascertained through probands with cardiovascular disease. Likelihood analysis supported recessive inheritance of high pump number. The major locus explained 14.0% of the variance in pump number; polygenic inheritance explained another 63.4%. Homozygotes for the recessive allele occurred with a frequency of 1.74% and had a mean pump number estimated as 566.0 sites/red blood cell (RBC) versus a mean of 312.2 sites/RBC for the other genotypes. Young individuals with the high pump number genotype were leaner, and older adults with the high pump number genotype were heavier. Diabetes and early hypertension were more prevalent in women with the high pump number genotype. Although not significant, obesity in adults of both sexes and early coronary heart disease in men were more prevalent in individuals with the high pump number genotype. 相似文献
969.
Syndiotactic polystyrene was efficiently prepared in the presence of a homogeneous catalyst composed of (η5-cyclopentadienyl)tribenzyloxytitanium and methylaluminoxane (MAO) as a cocatalyst. Influences of various polymerization conditions, e.g., [Ti]. [MAO], [St], temperature and the content of retained trimethylaluminium (TMA) in MAO on the catalytic activity, syndiotacticity and molecular weight of the polymer were studied. It was found that the retained TMA plays an important role in the polymerization. Lowering the retained TMA content in MAO decreases the activity of the catalyst remarkably. Addition of external alkylaluminium (TMA or triisobutylaluminium) into the catalyst system with MAO containing low amounts of retained TMA promotes styrene polymerization. 相似文献
970.
用体外琼脂培养法研究了PHA对小鼠骨髓CFU-GM的影响,结果表明,小鼠经腹腔注射PHA后,对小鼠CFU-GM产率和自杀率的影响随PHA的剂量不同而异,20~40mg/kg的PHA能明显提高CFU-GM的产率,其作用时间维持3天,剂量大于50mg/kg,可抑制CFU-GM产率。PHA组自杀率较对照组明显提高,提示适量的PHA在体内可促进小鼠CFU-GM的增殖,使更多的CFU-GM由Go期进入S期。将PHA直接加入无CSF的培养体系中,未见集落生长。此项结果提示PHA可能通过间接机制而非直接作用于CFU-GM。 相似文献