全文获取类型
收费全文 | 228488篇 |
免费 | 21382篇 |
国内免费 | 14448篇 |
专业分类
耳鼻咽喉 | 2172篇 |
儿科学 | 2580篇 |
妇产科学 | 2848篇 |
基础医学 | 26219篇 |
口腔科学 | 4032篇 |
临床医学 | 29013篇 |
内科学 | 32614篇 |
皮肤病学 | 2732篇 |
神经病学 | 11732篇 |
特种医学 | 8532篇 |
外国民族医学 | 106篇 |
外科学 | 24292篇 |
综合类 | 38903篇 |
现状与发展 | 56篇 |
一般理论 | 26篇 |
预防医学 | 16321篇 |
眼科学 | 5530篇 |
药学 | 24286篇 |
241篇 | |
中国医学 | 14009篇 |
肿瘤学 | 18074篇 |
出版年
2024年 | 905篇 |
2023年 | 3564篇 |
2022年 | 9283篇 |
2021年 | 11810篇 |
2020年 | 8991篇 |
2019年 | 7525篇 |
2018年 | 7932篇 |
2017年 | 7428篇 |
2016年 | 6921篇 |
2015年 | 10791篇 |
2014年 | 13090篇 |
2013年 | 12696篇 |
2012年 | 18457篇 |
2011年 | 19827篇 |
2010年 | 13159篇 |
2009年 | 10349篇 |
2008年 | 13220篇 |
2007年 | 12356篇 |
2006年 | 11782篇 |
2005年 | 11058篇 |
2004年 | 7382篇 |
2003年 | 6744篇 |
2002年 | 5473篇 |
2001年 | 4345篇 |
2000年 | 4408篇 |
1999年 | 4244篇 |
1998年 | 2503篇 |
1997年 | 2544篇 |
1996年 | 1979篇 |
1995年 | 1920篇 |
1994年 | 1652篇 |
1993年 | 1010篇 |
1992年 | 1394篇 |
1991年 | 1235篇 |
1990年 | 1003篇 |
1989年 | 938篇 |
1988年 | 840篇 |
1987年 | 701篇 |
1986年 | 526篇 |
1985年 | 463篇 |
1984年 | 266篇 |
1983年 | 214篇 |
1982年 | 144篇 |
1981年 | 174篇 |
1980年 | 127篇 |
1979年 | 153篇 |
1978年 | 99篇 |
1977年 | 86篇 |
1975年 | 71篇 |
1974年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
本文对60名女性海洛因依赖者与54名健康女性的月经、生育等女性生理机能和性心理及性行为进行调查分析。发现女性海洛因依赖者月经异常率为95.0%,显著高于对照组6.8%(P<0.001);海洛因对性欲和性行为影响明显,吸注海洛因成瘾后,35.0%性欲减退,58.3%性欲消失;性行为方式:吸毒前96.7%以性交为主,吸毒成瘾后仅15.0%以性交为主(P<0.001),85%以非性交接触为主;海洛因成瘾后性能力明显障碍,性交次数由吸毒前平均4.9±1.6次/周减少至平均0.4±0.2次/周(P<0.01)。结果表明:海洛因对女性生理机能和心理卫生具有明显损害作用。 相似文献
992.
Yang GC; Croaker D; Zhang AL; Manglick P; Cartmill T; Cass D 《Human molecular genetics》1998,7(6):1047-1052
Lethal white foal syndrome (LWFS) is a congenital anomaly of horses
characterized by a white coat colour and aganglionosis of the bowel, which
is similar to Hirschsprung disease (HSCR). We decided to investigate
possible mutations of the endothelin-B receptor gene ( EDNRB ) in LWFS as
recent studies in mutant rodents and some patients have demonstrated EDNRB
defects. First, we identified a full-length cDNA for horse EDNRB . This
cDNA fragment contained a 1329 bp open reading frame which encoded 443
amino acid residues. The predicted amino acid sequence was 89, 91 and 85%
identical to human, bovine and mouse as well as rat EDNRB respectively, but
only 55% identical to the human, bovine and rat endothelin A receptor
(EDNRA). Secondly, sequence analysis, together with allele-specific PCR and
the amplification- created restriction site (ACRS) technique, revealed a
dinucleotide TC-- >AG mutation, which changed isoleucine to lysine in
the predicted first transmembrane domain of the EDNRB protein. This was
associated with LWFS when homozygous and with the overo phenotype when
heterozygous.
相似文献
993.
G L Y Woo M L Yang H Q Yin F Jaffer M W Mittelman J P Santerre 《Journal of biomedical materials research》2002,59(1):35-45
Biomaterial-related infections continue to represent a significant challenge to the medical community. Several approaches have been utilized to incorporate antimicrobial agents at the surface of implant devices in attempts to delay or eliminate the formation of biofilms. To date, most of these strategies have focused on drug conjugation or diffusion-limited systems for the delivery of such pharmaceutical agents. More recently, work has been presented on the feasibility of incorporating drugs into the backbone of polymers as a main-chain monomer. When sequenced into the backbone of the polymer with other monomers that are hydrolytically sensitive to enzyme-catalyzed breakdown, it is thought that drugs may be able to be selectively released. Specifically, degradable polyurethanes have been synthesized with fluoroquinolone antibiotics and have shown an ability to kill bacteria when released following degradation of the polymer chains by the macrophage-derived enzyme cholesterol esterase. However, specificity of the cleavage sites in the polymer was difficult to control. Since cholesterol esterase has specificity for hydrophobic moieties, it is desirable to alter the formulation of the polyurethanes to incorporate long hydrophobic monomers immediately adjacent to the ciprofloxacin molecule. Hence, the current study focuses on evaluating the enzyme-catalyzed degradation of a degradable polyurethane synthesized with 1,12 diisocyanatododecane as a substitute for 1,6 diisocyanatohexane, which was used in previous work. Validation of specific ciprofloxacin release and the generation of antimicrobial are shown. A preliminary cell study to assess the cytotoxicity of this biodegradable antibiotic polymer shows that the material has no observable effects on cell proliferation or cell membrane structure. 相似文献
994.
Yang BZ Ding JH Zhou C Dimachkie MM Sweetman L Dasouki MJ Wilkinson J Roe CR 《Molecular genetics and metabolism》2000,69(3):259-262
A novel mutation was identified in two unrelated patients with medium-chain acyl-CoA dehydrogenase deficiency. First, a 19-year-old Caucasian female presented with a devastating illness, resulting in sudden death in adulthood which is unusual. The second patient, now a 3.5-year-old male, presented at 17 months of age with a hypoglycemic seizure and dehydration. Sequence analysis revealed a novel mutation G617T in exon 8 resulting in an arginine to leucine substitution at codon 206 (R206L). Both patients were compound heterozygous for this G617T and the common mutation A985G. 相似文献
995.
Yongxing Qiu Xiaojie Yu Linxian Feng Shilin Yang 《Macromolecular chemistry and physics.》1992,193(6):1377-1385
Using the rigid and hydrophobic polystyrene (PS) chain as backbone, onto which flexible and hydrophilic stearyl-poly(ethylene oxide) (SPEO) chains are grafted, a new kind of amphiphilic, microphase-separated graft copolymer was synthesized using the macromonomer technique. Stearyl-poly(ethylene oxide) macromonomers with acryloyl end-group (SPEO-A) were prepared through an end-group exchange reaction of α-stearyl-ω-hydroxypoly(ethylene oxide) (SPEO-OH) and acryloyl chloride in the presence of triethylamine. The radical copolymerization of styrene with SPEO-A was carried out under various experimental conditions. Following a careful examination of their purity, the structure of the prepared copolymers was characterized by means of IR, 1H NMR and GPC analyses. A new feasible method using first derivative UV spectrometry was developed for quantitative determination of the bulk composition of the graft copolymers. Copolymers with a wide range of bulk composition and satisfactory grafting degree were obtained. 相似文献
996.
Wen-Po Lin Hsing-Lung Lai Yi-Lin Liu Yin-Mei Chiung Chia-Yang Shiau Jun-Ming Han Chuen-Mi Yang Yu-Tien Liu 《Journal of microbiology, immunology, and infection》2005,38(5):320-326
A recombinant plasmid, pYL-1, containing a tyrosinase gene whose expression is under the control of a phage T5 promoter and 2 lac operators, was constructed. Escherichia coli JM109 harboring pYL-1 was used for production of bacterial melanin. A simple procedure for the isolation and purification of melanin was developed. The ultraviolet (UV)-visible light absorption spectra of melanin prepared by chemical synthesis and derived from different organisms, including bacteria, a plant and an animal source, were determined. Melanins produced by both bacteria and chemical synthesis showed a steady increase of absorption at wavelengths of UV light ranging from approximately 200-400 nm, while melanin derived either from plant or animal sources showed an additional discrete absorption peak at wavelength 280 nm upon a similar steady increase of absorption. This additional absorption peak could be due to the presence of protein-bound melanins in animal and plant sources while a free form of melanin was obtained from bacteria and chemical synthesis. Analysis of the effect of bacterial melanin on the activity of antibiotics against E. coli revealed that the activities of polymyxin B, kanamycin, tetracycline, and ampicillin were markedly reduced in the presence of melanin, whereas the activity of norfloxacin was not affected. The reduction of the antibacterial activity may result directly from the interaction of antibiotics with melanin. However, the mechanism of this interaction remains to be demonstrated. 相似文献
997.
998.
八珍汤对血虚模型小鼠造血调控因子影响的实验研究 总被引:7,自引:0,他引:7
探讨八珍汤对由环磷酰胺引起的小鼠骨髓造血功能抑制的调控作用。采用环磷酰胺致小鼠血虚模型 ,测定八珍汤对骨髓抑制小鼠外周血象及其细胞因子产生的影响。结果表明 ,八珍汤对环磷酰胺所致血虚模型小鼠骨髓细胞有促进增殖作用 ;经八珍汤诱导制备的巨噬细胞、脾细胞、肺条件培养液和骨骼肌条件培养液能促进血虚模型小鼠骨髓细胞增殖 ,促进血虚模型小鼠骨髓基质细胞分泌肿瘤坏死因子 (TNF)。八珍汤对环磷酰胺所致化疗损伤的造血调控作用可能与直接或间接刺激造血微环境的基质细胞分泌正性和负性造血生长因子有关。 相似文献
999.
Locomotion defects, together with Pins, regulates heterotrimeric G-protein signaling during Drosophila neuroblast asymmetric divisions 下载免费PDF全文
Heterotrimeric G proteins mediate asymmetric division of Drosophila neuroblasts. Free Gbetagamma appears to be crucial for the generation of an asymmetric mitotic spindle and consequently daughter cells of distinct size. However, how Gbetagamma is released from the inactive heterotrimer remains unclear. Here we show that Locomotion defects (Loco) interacts and colocalizes with Galphai and, through its GoLoco motif, acts as a guanine nucleotide dissociation inhibitor (GDI) for Galphai. Simultaneous removal of the two GoLoco motif proteins, Loco and Pins, results in defects that are essentially indistinguishable from those observed in Gbeta13F or Ggamma1 mutants, suggesting that Loco and Pins act synergistically to release free Gbetagamma in neuroblasts. Furthermore, the RGS domain of Loco can also accelerate the GTPase activity of Galphai to regulate the equilibrium between the GDP- and the GTP-bound forms of Galphai. Thus, Loco can potentially regulate heterotrimeric G-protein signaling via two distinct modes of action during Drosophila neuroblast asymmetric divisions. 相似文献
1000.
In this study we investigate the expression pattern of mucin genes in the human testis and evaluate the relationship between the expression of mucin genes and impaired spermatogenesis in the human testis. Thirty human testis tissues were collected from patients undergoing diagnostic testicular biopsy to investigate the cause of infertility. One part of the tissue underwent histological observation, and the other part of the tissue was subjected to semiquantitative RT-PCR of mucin genes, that is, mucin1, 2, 3, 4, and 9. The relative amount of mucin mRNAs was calculated by densitometry using glyceraldehydes-3-phosphate dehydrogenase (GAPDH) as an internal control. The samples were histologically diagnosed as either obstructive azoospermia with normal spermatogenesis (n = 13) or non-obstructive azoospermia with impaired spermatogenesis (n = 17). In the human testis with normal spermatogenesis, mRNA expression of mucin1, 9, 13 and GAPDH were found, but RT-PCR products of mucin 2, 3 and 4 were not detected. In the testis with impaired spermatogenesis, however, RT-PCR product of mucin1 was not found. There was no difference in the other mucin mRNA expression patterns between the testis with either normal or impaired spermatogenesis. To our knowledge, this study is the first that has detected the mRNA of mucin9 and 13 in human testis. This study also shows that mucin1 expression might be closely related to spermatogenesis. Our findings should be substantiated by more direct evidence, such as mucin protein expression and localization. 相似文献