全文获取类型
收费全文 | 19479篇 |
免费 | 1440篇 |
国内免费 | 1386篇 |
专业分类
22305篇 |
出版年
2024年 | 52篇 |
2023年 | 290篇 |
2022年 | 634篇 |
2021年 | 1067篇 |
2020年 | 712篇 |
2019年 | 897篇 |
2018年 | 807篇 |
2017年 | 622篇 |
2016年 | 885篇 |
2015年 | 1260篇 |
2014年 | 1482篇 |
2013年 | 1523篇 |
2012年 | 1762篇 |
2011年 | 1537篇 |
2010年 | 961篇 |
2009年 | 819篇 |
2008年 | 950篇 |
2007年 | 770篇 |
2006年 | 730篇 |
2005年 | 574篇 |
2004年 | 527篇 |
2003年 | 475篇 |
2002年 | 412篇 |
2001年 | 374篇 |
2000年 | 341篇 |
1999年 | 312篇 |
1998年 | 204篇 |
1997年 | 188篇 |
1996年 | 174篇 |
1995年 | 152篇 |
1994年 | 115篇 |
1993年 | 105篇 |
1992年 | 132篇 |
1991年 | 110篇 |
1990年 | 96篇 |
1989年 | 58篇 |
1988年 | 46篇 |
1987年 | 49篇 |
1986年 | 25篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
This study examined emotional modulation of word processing, showing that the recognition potential (RP), an ERP index of word recognition, could be modulated by different emotional states. In the experiment, participants were instructed to compete with pseudo-competitors, and via manipulation of the outcome of this competition, they were situated in neutral, highly positive, slightly positive, highly negative or slightly negative emotional states. They were subsequently asked to judge whether the referent of a word following a series of meaningless character segmentations was an animal or not. The emotional induction task and the word recognition task were alternated. Results showed that 1) compared with the neutral emotion condition, the peak latency of the RP under different emotional states was earlier and its mean amplitude was smaller, 2) there was no significant difference between RPs elicited under positive and negative emotional states in either the mean amplitude or latency, and 3) the RP was not affected by different degrees of positive emotional states. However, compared to slightly negative emotional states, the mean amplitude of the RP was smaller and its latency was shorter in highly negative emotional states over the left hemisphere but not over the right hemisphere. The results suggest that emotional states influence word processing. 相似文献
42.
Yue Zhang Xuanshi Liu Ruolan Guo Wenjian Xu Qi Guo Chanjuan Hao Xin Ni Wei Li 《Bioscience reports》2021,41(7)
Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental condition characterized by atypical social interaction and communication together with repetitive behaviors and restricted interests. The prevalence of ASD has been increased these years. Compelling evidence has shown that genetic factors contribute largely to the development of ASD. However, knowledge about its genetic etiology and pathogenesis is limited. Broad applications of genomics studies have revealed the importance of gene mutations at protein-coding regions as well as the interrupted non-coding regions in the development of ASD. In this review, we summarize the current evidence for the known molecular genetic basis and possible pathological mechanisms as well as the risk genes and loci of ASD. Functional studies for the underlying mechanisms are also implicated. The understanding of the genetics and genomics of ASD is important for the genetic diagnosis and intervention for this condition. 相似文献
43.
Knockdown of SLC34A2 inhibits cell proliferation,metastasis, and elevates chemosensitivity in glioma
Solute carrier 34 A2 (SLC34A2) is a member of SLC34 family that is a group of phosphate transporters. SLC34A2 has been reported to play critical roles in tumorigenesis and progression. However, the researches about the biological roles of SLC34A2 in glioma have not yet been reported. In this study, we analyzed the expression patterns of SLC34A2 in clinical glioma tumor tissues and cell lines. The results demonstrated that SLC34A2 was generally overexpressed in both glioma tissues and cell lines. To further investigate the roles of SLC34A2 in glioma, lentivirus containing specific SLC34A2 short hairpin RNA (sh-SLC34A2) was used to infect glioma cell lines U251 and U87 for the knockdown of SLC34A2. The following studies proved that SLC34A2 knockdown exhibited suppressive effects on cell proliferation and migration/invasion. SLC34A2 knockdown also inhibited epithelial-mesenchymal transition (EMT) phenotype, as evidenced by the increased E-cadherin expression, and the decreased N-cadherin and fibronectin expressions. Besides, knockdown of SLC34A2 enhanced the temozolomide (TMZ) sensitivity of U251 and U87 cells. In vivo tumorigenicity assay demonstrated that SLC34A2 knockdown inhibited tumor growth. Moreover, SLC34A2 knockdown suppressed the activation of epidermal growth factor receptor (EGFR)/PI3K/AKT signaling pathway in U87 cells. GW2974 (EGFR inhibitor) increased SLC34A2 knockdown-inhibited cell proliferation, migration/invasion, as well as enhanced SLC34A2 knockdown-increased the TMZ sensitivity of glioma cells. These findings suggested that SLC34A2 might be a new potential therapeutic target for the therapy of glioma patients. 相似文献
44.
J Clulow S Clulow J Guo AJ French MJ Mahony M Archer 《Reproductive biology and endocrinology : RB&E》2012,10(1):60
ABSTRACT: BACKGROUND: Protocols for the hormonal induction of ovulation and oviposition are essential tools for managing threatened amphibians with assisted reproduction, but responses vary greatly between species and even broad taxon groups. Consequently, it is necessary to assess effectiveness of such protocols in representative species when new taxa become targets for induction. The threatened genus Mixophyes (family Myobatrachidae) has amongst the highest proportion of endangered species of all the Australian amphibians. This study developed and optimised the induction of oviposition in a non-threatened member of this taxon, the great barred frog (Mixophyes fasciolatus). METHODS: Gravid female M. fasciolatus were induced to oviposit on one or more occasions by administration of human chorionic gonadotropin (hCG) with or without priming with pregnant mare serum gonadotropin (PMSG). Treatments involved variations in hormone doses and combinations (administered via injection into the dorsal lymph sacs), and timing of administration. Pituitary homogenates from an unrelated bufonid species (Rhinella marina) were also examined with hCG. RESULTS: When injected alone, hCG (900 to 1400 IU) induced oviposition. However, priming with two time dependent doses of PMSG (50 IU, 25 IU) increased responses, with lower doses of hCG (200 IU). Priming increased response rates in females from around 30% (hCG alone) to more than 50% (p = 0.035), and up to 67%. Increasing the interval between the first PMSG dose and first hCG dose from 3 to 6 days also produced significant improvement (p<0.001). Heterologous pituitary extracts administered with hCG were no more effective than hCG alone (p = 0.628). CONCLUSIONS: This study found that M. fasciolatus is amongst the few amphibian species (including Xenopus (Silurana) and some bufonids) that respond well to the induction of ovulation utilising mammalian gonadotropins (hCG). The optimal protocol for M. fasciolatus involved two priming doses of PMSG (50 IU and 25 IU) administered at 6 and 4 days respectively, prior to two doses of hCG (100 IU), 24 hours apart. This study is also the first to demonstrate in an amphibian species that responds to mammalian gonadotropins that an increase in the ovulation rate occurs after priming with a gonadotropin (PMSG) with FSH activity. 相似文献
45.
46.
Background
Epidemiological evidence suggests that vitamin D deficiency is linked to various chronic diseases. However direct measurement of serum 25-hydroxyvitamin D (25(OH)D) concentration, the accepted biomarker of vitamin D status, may not be feasible in large epidemiological studies. An alternative approach is to estimate vitamin D status using a predictive model based on parameters derived from questionnaire data. In previous studies, models developed using Multiple Linear Regression (MLR) have explained a limited proportion of the variance and predicted values have correlated only modestly with measured values. Here, a new modelling approach, nonlinear radial basis function support vector regression (RBF SVR), was used in prediction of serum 25(OH)D concentration. Predicted scores were compared with those from a MLR model.Methods
Determinants of serum 25(OH)D in Caucasian adults (n = 494) that had been previously identified were modelled using MLR and RBF SVR to develop a 25(OH)D prediction score and then validated in an independent dataset. The correlation between actual and predicted serum 25(OH)D concentrations was analysed with a Pearson correlation coefficient.Results
Better correlation was observed between predicted scores and measured 25(OH)D concentrations using the RBF SVR model in comparison with MLR (Pearson correlation coefficient: 0.74 for RBF SVR; 0.51 for MLR). The RBF SVR model was more accurately able to identify individuals with lower 25(OH)D levels (<75 nmol/L).Conclusion
Using identical determinants, the RBF SVR model provided improved prediction of serum 25(OH)D concentrations and vitamin D deficiency compared with a MLR model, in this dataset. 相似文献47.
Biobased poly(propylene sebacate) as shape memory polymer with tunable switching temperature for potential biomedical applications 总被引:2,自引:0,他引:2
From the point of better biocompatibility and sustainability, biobased shape memory polymers (SMPs) are highly desired. We used 1,3-propanediol, sebacic acid, and itaconic acid, which have been industrially produced via fermentation or extraction with large quantities as the main raw materials for the synthesis of biobased poly(propylene sebacate). Diethylene glycol was used to tailor the flexibility of the polyester. The resulted polyesters were found to be promising SMPs with excellent shape recovery and fixity (near 100% and independent of thermomechanical cycles). The switching temperature and recovery speed of the SMPs are tunable by controlling the composition of the polyesters and their curing extent. The continuously changed switching temperature ranging from 12 to 54 °C was realized. Such temperature range is typical for biomedical applications in the human body. The molecular and crystalline structures were explored to correlate to the shape memory behavior. The combination of potential biocompatibility and biodegradability of the biobased SMPs makes them suitable for fabricating biomedical devices. 相似文献
48.
49.
Ying‐Ying Wang Bao‐Hua Hou Jin‐Zhi Guo Qiu‐Li Ning Wei‐Lin Pang Jiawei Wang Chang‐Li Lü Xing‐Long Wu 《Liver Transplantation》2018,8(18)
Presently, commercialization of sodium‐ion batteries (SIBs) is still hindered by the relatively poor energy‐storage performance. In addition, low‐temperature (low‐T) Na storage is another principal concern for the wide application of SIBs. Unfortunately, the Na‐transfer kinetics is extremely sluggish at low‐T, as a result, there are few reports on low‐T SIBs. Here, an advanced low‐T sodium‐ion full battery (SIFB) assembled by an anode of 3D Se/graphene composite and a high‐voltage cathode (Na3V2(PO4)2O2F) is developed, exhibiting ultralong lifespan (over even 15 000 cycles, the capacity retention is still up to 86.3% at 1 A g?1), outstanding low‐T energy storage performance (e.g., all values of capacity retention are >75% after 1000 cycles at temperatures from 25 to ?25 °C at 0.4 A g?1), and high‐energy/power properties. Such ultralong lifespan signifies that the developed sodium‐ion full battery can be used for longer than 60 years, if batteries charge/discharge once a day and 80% capacity retention is the standard of battery life. As a result, the present study not only promotes the practicability and commercialization of SIBs but also points out the new developing directions of next‐generation energy storage for wider range applications. 相似文献
50.
Due to the regulations and bans regarding the use of traditional toxic chemicals against marine fouling organisms and the
practical impediments to the commercialization of natural product antifoulants, there is an urgent need for compounds that
are antifouling-active, environmentally friendly, and have a potential for commercial application. In this study, a series
of common, commercially available pyrethroid products, which are generally used as environmentally safe insecticides, was
evaluated for antifouling activity in the laboratory using an anti-settlement test with cyprids of the barnacle Balanus albicostatus and also in a field experiment. Laboratory assay showed that all eleven pyrethroids (namely, rich d-trans-allethrin, Es-biothrin, rich d-prallethrin, S-prallethrin, tetramethrin, rich d-tetramethrin, phenothrin, cyphenothrin, permethrin, cypermethrin, and high active cypermethrin) were able to inhibit barnacle
settlement (EC50 range of 0.0316 to 87.00 μg/ml) without significant toxicity. Analysis of structure–activity relationships suggested that
the cyano group at the α-carbon position had a significant influence on the expression of antifouling activity in pyrethroids.
In the field, the antifouling activity of pyrethroids was further confirmed, with the most potent pyrethroids being cypermethrin
and high active cypermethrin, which displayed efficiency comparable with that of tributyltin. In summary, our investigation
indicated that these pyrethroids have a great and practical commercial potential as antifouling agents. 相似文献