全文获取类型
收费全文 | 42205篇 |
免费 | 3445篇 |
国内免费 | 1273篇 |
专业分类
耳鼻咽喉 | 306篇 |
儿科学 | 244篇 |
妇产科学 | 204篇 |
基础医学 | 2483篇 |
口腔科学 | 557篇 |
临床医学 | 3929篇 |
内科学 | 2676篇 |
皮肤病学 | 451篇 |
神经病学 | 1694篇 |
特种医学 | 1318篇 |
外国民族医学 | 7篇 |
外科学 | 1777篇 |
综合类 | 9713篇 |
现状与发展 | 5篇 |
预防医学 | 5077篇 |
眼科学 | 657篇 |
药学 | 8525篇 |
495篇 | |
中国医学 | 4877篇 |
肿瘤学 | 1928篇 |
出版年
2024年 | 101篇 |
2023年 | 545篇 |
2022年 | 1151篇 |
2021年 | 1815篇 |
2020年 | 1985篇 |
2019年 | 1048篇 |
2018年 | 1073篇 |
2017年 | 1568篇 |
2016年 | 2166篇 |
2015年 | 1916篇 |
2014年 | 4030篇 |
2013年 | 3670篇 |
2012年 | 3178篇 |
2011年 | 2913篇 |
2010年 | 2241篇 |
2009年 | 1899篇 |
2008年 | 1772篇 |
2007年 | 1877篇 |
2006年 | 1622篇 |
2005年 | 1376篇 |
2004年 | 1042篇 |
2003年 | 964篇 |
2002年 | 821篇 |
2001年 | 730篇 |
2000年 | 568篇 |
1999年 | 538篇 |
1998年 | 436篇 |
1997年 | 367篇 |
1996年 | 344篇 |
1995年 | 332篇 |
1994年 | 299篇 |
1993年 | 235篇 |
1992年 | 246篇 |
1991年 | 220篇 |
1990年 | 199篇 |
1989年 | 200篇 |
1988年 | 191篇 |
1987年 | 143篇 |
1986年 | 144篇 |
1985年 | 175篇 |
1984年 | 135篇 |
1983年 | 91篇 |
1982年 | 104篇 |
1981年 | 74篇 |
1980年 | 60篇 |
1979年 | 71篇 |
1978年 | 53篇 |
1977年 | 59篇 |
1976年 | 40篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Sleep plays a role in strengthening new words and integrating them with existing vocabulary knowledge, consistent with neural models of learning in which sleep supports hippocampal transfer to neocortical memory. Such models are based on adult research, yet neural maturation may mean that the mechanisms supporting word learning vary across development. Here, we propose a model in which children may capitalise on larger amounts of slow-wave sleep to support a greater demand on learning and neural reorganisation, whereas adults may benefit from a richer knowledge base to support consolidation. Such an argument is reinforced by the well-reported “Matthew effect”, whereby rich vocabulary knowledge is associated with better acquisition of new vocabulary. We present a meta-analysis that supports this association between children’s existing vocabulary knowledge and their integration of new words overnight. Whilst multiple mechanisms likely contribute to vocabulary consolidation and neural reorganisation across the lifespan, we propose that contributions of existing knowledge should be rigorously examined in developmental studies. Such research has potential to greatly enhance neural models of learning. 相似文献
992.
目的探讨漂浮导管技术应用于急性心功能衰竭患者的临床效果、指导意义。方法 2007年5月~2010年12月入住我科ICU的75例急性心衰患者中35例患者在漂浮导管监测下给予常规心衰治疗,另40例患者未予漂浮导管监测下给予经验性常规心衰治疗,比较两组患者治疗前后的病情缓解时间。结果 35例在漂浮导管监测指导下治疗的患者较未予漂浮导管监测治疗的患者病情缓解时间短、心衰并发症发生率低(P〈0.05)。结论漂浮导管技术对于血流动力学不稳定的急性心力衰竭患者的临床治疗有重要的指导价值。 相似文献
993.
目的研究天茄子不同提取部位的止血药理作用。方法依次以环己烷(T1)、水(T2)和乙醇(T3)为溶剂进行提取并对乙醇提取物依次用石油醚(T4)、乙酸乙酯(T5)、正丁醇(T6)进行萃取得到相应的部位以及水部位(T7),采用毛细玻管法、玻片法、剪尾法和测定血浆复钙时间检测其止血作用。结果 T3、T6、T7可缩短小鼠玻片法凝血时间,T3、T5、T6、T7可显著缩短小鼠毛细管法凝血时间,T3、T4、T5、T6、T7可显著缩短小鼠断尾法出血时间,T3、T6、T7可显著缩短小鼠血浆复钙时间。结论天茄子95%醇总提物、乙酸乙酯部位、正丁醇部位、水部位凝血效果显著,其中95%醇总提物、正丁醇部位、水部位凝血效果极其显著。 相似文献
994.
995.
目的观察水性伤痛贴治疗慢性腰腿痛的临床疗效。方法对256例门诊慢性腰腿痛患者使用水性伤痛贴进行外敷治疗,对治疗前后的症状、体征进行综合疗效评价。结果治愈率为21.1%;显效率为40.2%;有效率为34.8%;无效率为3.9%;总有效率为96.1%。结论水性伤痛贴在慢性腰腿痛的治疗方面有明显的止痛、消肿作用,临床效果明显。 相似文献
996.
997.
Histological studies of the effects of oral administration of extract of Aspilia africana, used in ethno medical practice in Africa for the management of various ailments, on the ovarian tissues of matured female Wistar rats were studied. The rats (n=24), average weight 182g were randomly assigned into two treatment (n=16) and a control (n=8) group. The rats in the treatment groups received 0.5g/kg and 1g/kg of aqueous extract of Aspilia africana orally through orogastric tube for fourteen days, while the control rats received equal volume of distilled water without the extract of Aspilia added. The rats were fed with growers'' mash and were given water liberally. The rats were sacrificed on day fifteen of the experiment. The ovary was carefully dissected out and quickly fixed in 10% formal saline for routine histological study after H&E method. The histological findings indicated that the treated sections of the ovary showed cellular hypertrophy of the theca folliculi, distortion of the basement membrane, degenerative and atrophic changes in the oocyte and zona granulosa. There were marked vacuolations appearing in the stroma cells. These findings indicate that Aspilia africana consumption may probably have adverse effects on the ovaries by its deleterious effects on the oocytes and stroma cells of ovary of adult Wistar rats. It is recommended that further studies aimed at corroborating these observations be conducted. 相似文献
998.
Farghalli A. Mohamed 《Materials》2011,4(7):1194-1223
Micrograin Superplasticity refers to the ability of fine-grained materials (1 µm < d < 10 μm, where d is the grain size) to exhibit extensive neck-free elongations during deformation at elevated temperatures. Over the past three decades, good progress has been made in rationalizing this phenomenon. The present paper provides a brief review on this progress in several areas that have been related to: (a) the mechanical characteristics of micrograin superplasticity and their origin; (b) the effect of impurity content and type on deformation behavior, boundary sliding, and cavitation during superplastic deformation; (c) the formation of cavity stringers; (d) dislocation activities and role during superplastic flow; and (e) the utilization of superplasticity. 相似文献
999.
Likun Gao Xun Cui Zewei Wang Christopher D. Sewell Zili Li Shuang Liang Mingyue Zhang Jian Li Yingjie Hu Zhiqun Lin 《Proceedings of the National Academy of Sciences of the United States of America》2021,118(7)
The ability to develop highly active and low-cost electrocatalysts represents an important endeavor toward accelerating sluggish water-oxidation kinetics. Herein, we report the implementation and unraveling of the photothermal effect of spinel nanoparticles (NPs) on promoting dynamic active-sites generation to markedly enhance their oxygen evolution reaction (OER) activity via an integrated operando Raman and density functional theory (DFT) study. Specifically, NiFe2O4 (NFO) NPs are first synthesized by capitalizing on amphiphilic star-like diblock copolymers as nanoreactors. Upon the near-infrared light irradiation, the photothermal heating of the NFO-based electrode progressively raises the temperature, accompanied by a marked decrease of overpotential. Accordingly, only an overpotential of 309 mV is required to yield a high current density of 100 mA cm−2, greatly lower than recently reported earth-abundant electrocatalysts. More importantly, the photothermal effect of NFO NPs facilitates surface reconstruction into high-active oxyhydroxides at lower potential (1.36 V) under OER conditions, as revealed by operando Raman spectroelectrochemistry. The DFT calculation corroborates that these reconstructed (Ni,Fe)oxyhydroxides are electrocatalytically active sites as the kinetics barrier is largely reduced over pure NFO without surface reconstruction. Given the diversity of materials (metal oxides, sulfides, phosphides, etc.) possessing the photo-to-thermal conversion, this effect may thus provide a unique and robust platform to boost highly active surface species in nanomaterials for a fundamental understanding of enhanced performance that may underpin future advances in electrocatalysis, photocatalysis, solar-energy conversion, and renewable-energy production.Motivated by the need for accelerating sluggish reaction kinetics at the anode (1, 2), the focus of water electrolysis has been centered heavily on oxygen evolution reaction (OER) toward sustainable hydrogen fuel production. To date, there has been much effort in developing low-cost yet high-performance earth-abundant transition-metal alternatives to commonly used noble metals for OER. Intriguingly, many Ni-, Co-, Fe-, and Mn-based oxides experience a dynamic surface-reconstruction process to form more active oxyhydroxides, which are recognized as true catalytically active species for OER in alkaline media (3, 4). Among various transition metal-based OER catalysts, bimetal spinel-structured oxides in the form of AB2O4 (A and B are different metal ions) have garnered much attention due to their rich compositions, electron configurations, and valence states (5). Interestingly, inverse spinel NiFe2O4 (NFO), in principle, exhibits enhanced catalytic activity toward OER because of the presence of multivalent elements (i.e., Ni3+/Ni2+ and Fe3+/Fe2+) (6). It is important to note that studies on facilitating the surface reconstruction of NFO to achieve high-performance OER are relatively few, and a fundamental understanding as to what makes the derived OER catalysts perform well remains elusive.Recently, introducing thermal energy to promote electrocatalytic conversion has attracted significant interest (7–10). The thermal energy could accelerate the motion of reactant molecules, promote their effective collisions during the reaction, and thus make it easier to overcome the activation barrier (11, 12). Moreover, the use of thermal energy could also promote the surface reconstruction of catalysts into highly active species and accelerate the electrocatalytic kinetics, thereby leading to improved efficiency (13). Electrocatalysts with photothermal effect (referred to as photothermal electrocatalysts) enable in situ heating due to photo-to-thermal conversion under illumination with visible or near-infrared (NIR) light, thereby dispensing with the need for extra devices required to provide thermal energy. More importantly, in sharp contrast to common approaches where the entire solution is heated (14), the photothermal effect is localized on electrocatalysts themselves (15), thus effectively enabling heat modulation to a defined region (i.e., the working electrode). Despite recent impressive advances in transition metal oxides (e.g., Fe3O4 and Co3O4) as photothermal agents for cancer therapy (15), their implementations for photothermal-assisted OER, in particular spinel oxides, are comparatively few and limited in scope. Moreover, it has been reported that Ni- and Co-based OER catalysts are prone to surface reconstruction into highly active oxyhydroxides (16, 17). Surprisingly, the photothermal effect on promoting surface reconstruction in spinel oxide catalysts has yet to be explored.Herein, we report an integrated operando Raman and density functional theory (DFT) plus Hubbard U (DFT + U) study to exercise and unveil the photo-to-thermal conversion of inverse spinel oxide nanoparticles (NPs) in promoting the generation of dynamic active sites via surface reconstruction into oxyhydroxides and thus greatly enhancing their OER activity. First, a series of amphiphilic star-like poly(acrylic acid)-block-poly(styrene-co-acrylonitrile) (denoted PAA-b-PSAN) diblock copolymers with a well-defined molecular weight (MW) and low polydispersity index (PDI) are exploited as nanoreactors to synthesize a set of PSAN-ligated NFO NPs with different sizes and PSAN chain lengths. The effects of the NFO NP sizes and the outer PSAN chain lengths on catalytic activity of NFO NPs are then scrutinized. Interestingly, NFO NPs of the largest size (∼12 nm) ligated with the shortest PSAN chains (Mn = 7K) display the best OER reactivity on a glassy carbon (GC) electrode in alkaline media as a result of the high fraction of the exposed electrochemically active surface area and the fastest electrocatalytic kinetics. Subsequently, the photothermal effect of PSAN-ligated NFO NPs is exploited to promote their surface reconstruction and thus boost OER. More importantly, an operando Raman spectroelectrochemistry study is performed to unveil the mechanism of photothermal-assisted enhancement in OER reaction, revealing the emergence of electrocatalytically active γ-NiOOH at a lower potential (1.36 V) during the surface-reconstruction process with a photothermal effect. Finally, the first-principle calculations substantiate that the reconstructed surface, i.e., (Ni,Fe)oxyhydroxides, plays a pivotal role as the active site for electrocatalytic reaction. As such, photothermal electrocatalysts (e.g., metal oxides, sulfides, phosphides, etc.) may render significantly low overpotential and fast OER kinetics, representing an array of important materials that couple the localized heating with electrochemistry for effective renewable-energy production. 相似文献
1000.
Erito Mochiki Hideki Suzuki Seiichi Takenoshita Yukio Nagamachi Hiroyuki Kuwano Akiyoshi Mizumoto Zen Itoh 《Journal of gastroenterology》1998,33(6):835-841
Glucagon is commonly used during gastrointestinal examinations for the temporary inhibition of gastroduodenal movements.
Three preparations of glucagon are now clinically available: those prepared by extraction from the pancreas (GL-P), by chemical
synthesis (GL-S), and by genetic recombination (GL-G). The aim of this study was examine the mechanism of the inhibitory effect
of glucagon on gastrointestinal motility and the cause of its side effects by comparing three glucagon preparations. In four
conscious dogs, gastrointestinal contractions were monitored by means of chronically implanted force transducers. Each glucagon
preparation (GL-P [15 μg/kg], GL-S [5, 15, 45 μg/kg], GL-G [15 μg/kg]), scopolamine butylbromide (0.4 mg/kg), or saline was
administered intravenously 20 min after the termination of spontaneous phase III contractions, and blood samples were taken
at 5- to 10-min intervals. Barium was administered into the stomach 10 min after the infusion of each drug. The arrival of
a barium meal in the stomach immediately stimulated gastrointestinal contractions, and the barium meal was expelled into the
duodenum and jejunum from the stomach. Intravenous injection of 15 μg GL-S first stimulated duodenal contractions that propagated
to the jejunum, followed by strong inhibition of the barium-induced gastrointestinal contractions. This inhibitory effect
of glucagon and the activity of the glucagon-induced duodenal contractions were dose-related. The inhibitory effects of GL-G
and GL-S were stronger than that of GL-P. Blood glucose and plasma insulin concentrations were raised after intravenous injection
of each glucagon preparation, but there was no difference among the three preparations and no dose relationship. The inhibitory
effects of glucagon depend on the material purity and dose, and the inhibitory mechanism was independent of any effect on
carbohydrate metabolism. Glucagon administration caused phase III-like contractions in the duodenum and jejunum, which may
be responsible for the side effects of glucagon.
(Received Jan. 8, 1998; accepted June 26, 1998) 相似文献