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   8724篇
  免费   468篇
  国内免费   67篇
耳鼻咽喉   104篇
儿科学   119篇
妇产科学   74篇
基础医学   1146篇
口腔科学   214篇
临床医学   477篇
内科学   2205篇
皮肤病学   234篇
神经病学   720篇
特种医学   411篇
外科学   1662篇
综合类   48篇
一般理论   1篇
预防医学   202篇
眼科学   79篇
药学   447篇
中国医学   22篇
肿瘤学   1094篇
  2024年   7篇
  2023年   80篇
  2022年   138篇
  2021年   297篇
  2020年   135篇
  2019年   215篇
  2018年   258篇
  2017年   205篇
  2016年   275篇
  2015年   266篇
  2014年   326篇
  2013年   353篇
  2012年   569篇
  2011年   650篇
  2010年   372篇
  2009年   347篇
  2008年   512篇
  2007年   598篇
  2006年   557篇
  2005年   578篇
  2004年   510篇
  2003年   470篇
  2002年   490篇
  2001年   90篇
  2000年   70篇
  1999年   94篇
  1998年   107篇
  1997年   115篇
  1996年   73篇
  1995年   83篇
  1994年   37篇
  1993年   53篇
  1992年   40篇
  1991年   34篇
  1990年   40篇
  1989年   25篇
  1988年   29篇
  1987年   25篇
  1986年   14篇
  1985年   12篇
  1984年   8篇
  1983年   14篇
  1982年   12篇
  1981年   10篇
  1980年   10篇
  1979年   10篇
  1978年   11篇
  1975年   4篇
  1974年   7篇
  1967年   5篇
排序方式: 共有9259条查询结果,搜索用时 31 毫秒
991.

Purpose

The purpose of this study is to examine the clinical outcomes of blastocysts derived from human single-pronucleate (1PN) embryos after conventional in vitro fertilization (cIVF) and intracytoplasmic sperm injection (ICSI) cycles.

Methods

This was a retrospective study at a reproductive center of a hospital. To evaluate embryo quality and clinical outcomes, cIVF or ICSI cycles with one or more 1PN embryos were compared with same cycles with 2PN embryos (control cycles).

Results

A total of 623 cycles (426 cIVF cycles and 197 ICSI cycles) were treated with cIVF or ICSI. The single pronuclear status rate was similar between cIVF (22.1 %) and ICSI (25.1 %) cycles. Although the development rates of 1PN embryos on day 3 and day 5/6 in cIVF were significantly higher than those in ICSI, those of 1PN embryos in cIVF were significantly lower compared to 2PN embryos (p < 0.01). Nonetheless, the ongoing pregnancy rates achieved with 1PN blastocysts in 1PN embryos did not significantly differ from the control group. Thirty-three transfer cycles with 33 blastocysts derived from 1PN embryos in cIVF resulted in nine deliveries with no newborn malformations; however, no implantation was observed in three ICSI cycles.

Conclusion

Although the blastocyst formation rate of 1PN embryos was significantly lower than 2PN embryos in cIVF and ICSI cycles, 1PN blastocysts in cIVF, and not from ICSI, demonstrated an adequate ongoing pregnancy rate. These results suggested that 1PN blastocysts in cIVF are available for clinical use and may lead to an increase in the chance of pregnancy in patients receiving assisted reproductive technology with 1PN embryos.  相似文献   
992.
Using the Japan Meteorological Agency earthquake catalog, we investigate the seismicity variations before major earthquakes in the Japanese region. We apply natural time, the new time frame, for calculating the fluctuations, termed β, of a certain parameter of seismicity, termed κ1. In an earlier study, we found that β calculated for the entire Japanese region showed a minimum a few months before the shallow major earthquakes (magnitude larger than 7.6) that occurred in the region during the period from 1 January 1984 to 11 March 2011. In this study, by dividing the Japanese region into small areas, we carry out the β calculation on them. It was found that some small areas show β minimum almost simultaneously with the large area and such small areas clustered within a few hundred kilometers from the actual epicenter of the related main shocks. These results suggest that the present approach may help estimation of the epicentral location of forthcoming major earthquakes.In this study, we investigate the evolution of seismicity shortly before main shocks in the Japanese region, N2546E125148, using Japan Meteorological Agency (JMA) earthquake catalog as in ref 1. For this, we adopted the new time frame called natural time since our previous works using this time frame made the lead time of prediction as short as a few days (see below). For a time series comprising N earthquakes (EQs), the natural time χk is defined as χkk/N, where k means the kth EQ with energy Qk (Fig. 1). Thus, the raw data for our investigation, to be read from the earthquake catalog, are χkk/N and pk=Qk/n=1NQn, where pk is the normalized energy. In natural time, we are interested in the order and energy of events but not in the time intervals between events.Open in a separate windowFig. 1.EQ sequence in (A) conventional time and (B) natural time. In B, Qk is given in units of the energy ε corresponding to a 3.5MJMA EQ.We first calculate a parameter called κ1, which is defined as follows (2, 3), from the catalog.κ1=k=1Npkχk2(k=1Npkχk)2=χ2χ2.[1]We start the calculation of κ1 at the time of initiation of Seismic Electric Signals (SES), the transient changes of the electric field of Earth that have long been successfully used for short-term EQ prediction (4, 5). The area to suffer a main shock is estimated on the basis of the selectivity map (4, 5) of the station that recorded the corresponding SES. Thus, we now have an area in which we count the small EQs of magnitude greater than or equal to a certain magnitude threshold that occur after the initiation of the SES. We then form time series of seismic events in natural time for this area each time a small EQ occurs, in other words, when the number of the events increases by one. The κ1 value for each time series is computed for the pairs (χk,pk) by considering that χk is “rescaled” to χk = k/(N +1) together with rescaling pk=Qk/n=1N+1Qn upon the occurrence of any additional event in the area. The resulting number of thus computed κ1 values is usually of the order 102 to 103 depending, of course, on the magnitude threshold adopted for the events that occurred after the SES initiation until the main shock occurrence. When we followed this procedure, it was found empirically that the values of κ1 converge to 0.07 a few days before main shocks. Thus, by using the date of convergence to 0.07 for prediction, the lead times, which were a few months to a few weeks or so by SES data alone, were made, although empirically, as short as a few days (6, 7). In fact, the prominent seismic swarm activity in 2000 in the Izu Island region, Japan, was preceded by a pronounced SES activity 2 mo before it, and the approach of κ1 to 0.07 was found a few days before the swarm onset (8). However, when SES data are not available, which is usually the case, it is not possible to follow the above procedure. To cope with this difficulty, in the previous work (1), we investigated the time change of the fluctuation of the κ1 values during a few preseismic months for each EQ (which we call target EQ) over the large area N2546E125148 (Fig. 2A) for the period from 1 January 1984 to 11 March 2011, the day of M9.0 Tohoku EQ. Setting a threshold MJMA = 3.5 to assure data completeness of JMA catalog, we were left with 47,204 EQs in the concerned period of about 326 mo: ∼150 EQs per month. For calculating the β values, we chose 200 EQs before target EQs to cover the seismicity in almost one and a half months.Open in a separate windowFig. 2.(A) The 47,204 EQs with MJMA ≥ 3.5 that occurred during the period of our study. (B) Contours of the number of EQs per month within R = 250 km. Solid diamonds show the epicenters of six shallow EQs investigated in this study. (C) Contours of the natural time window W used in each of the 12,476 areas of radius R = 250 km with offset 0.1° from one another that have at least eight EQs per month.To obtain the fluctuation β of κ1, we need many values of κ1 for each target EQ. For this purpose, we first took an excerpt comprised of W successive EQs just before a target EQ from the seismic catalog. The number W was chosen to cover a period of a few months. For this excerpt, we form its subexcerpts Sj={Qj+k1}k=1,2,,N of consecutive N = 6 EQs (since at least six EQs are needed (2) for obtaining reliable κ1) of energy Qj+k?1 and natural time χkk/N each. Further, pk=Qj+k1/k=1NQj+k1, and by sliding Sj over the excerpt of W EQs, j=1,2,,WN+1 (= W − 5), we calculate κ1 using Eq. 1 for each j. We repeat this calculation for N=7,8,,W, thus obtaining an ensemble of [(W − 4)(W − 5)]/2 (= 1 + 2 +…+ W − 5) κ1 values. Then, we compute the average μ(κ1) and the SD σ(κ1) of thus obtained ensemble of [(W − 4)(W − 5)]/2 κ1 values. The variability β of κ1 for this excerpt W is defined to be β ≡ σ(κ1)/μ(κ1) and is assigned to the (W + 1)th EQ, i.e., the target EQ.The time evolution of the β value can be pursued by sliding the excerpt through the EQ catalog. Namely, through the same process as above, β values assigned to (W + 2)th, (W + 3)th, … EQs in the catalog can be obtained.We found in ref. 1 that the fluctuation β of κ1 values exhibited minimum a few months before all of the six shallow EQs of magnitude larger than 7.6 that occurred in the study period. A minimum of β ≡ σ(κ1)/μ(κ1) means large average and/or small deviation of κ1 values (e.g., see ref. 9).In the present work, we calculate the β values for small areas before the six large EQs, which showed β minima of the large area.  相似文献   
993.
OBJECTIVES: We aimed to establish an enzyme-linked immunosorbent assay (ELISA) for measuring soluble elastin fragments (sELAF) in serum and to reveal its usefulness in diagnosing acute aortic dissection. BACKGROUND: Acute aortic dissection is a life-threatening disease of the aorta. However, the diagnosis is still frequently missed, especially at onset. The establishment and clinical availability of simplified laboratory test(s) to help diagnose and screen acute aortic dissection patients is therefore urgently needed. METHODS and RESULTS: An ELISA to measure sELAF in serum was developed using the newly created double monoclonal antibodies which recognize the different epitopes of human aortic elastin. Twenty-five acute aortic dissection patients, 50 patients with acute myocardial infarction, and 474 healthy individuals were enrolled in the study. The sELAF levels from healthy subjects gradually increased with aging. When the cutoff point for positivity was set at the mean + 3SD above the mean of those in healthy subjects at each age, 16 acute aortic dissection patients (64.0%) were found to be positive, while only one acute myocardial infarction patient was positive (2.0%). Acute aortic dissection patients with either an open or a partially open pseudolumen were found to be 88.9% positive for sELAF, while those with its early closure was 0% positive. The difference in the sELAF levels between acute aortic dissection patients with and without a thrombotic closure of false lumen was significant (60.3 +/- 15.6 vs 135.4 +/- 53.2 ng/ml, p < 0.005). CONCLUSIONS: The sELAF level in serum may be a useful marker for helping both diagnose and screen acute aortic dissection, while also helping distinguish acute aortic dissection from acute myocardial infarction.  相似文献   
994.
995.
A recombinant hepatitis B virus (HBV) expressing NanoLuc (NL) (HBV/NL) was produced by cotransfecting a plasmid containing a 1.2‐fold HBV genome carrying the NL gene with a plasmid bearing a packaging‐defective 1.2‐fold HBV genome into a human hepatoma cell line, HepG2. We found that NL activity in HBV/NL‐infected primary hepatocytes or sodium taurocholate cotransporting polypeptide‐transduced human hepatocyte‐derived cell lines increased linearly for several days after infection and was concordant with HBV RNA levels in the cells. Treatment of the virus‐infected cells with HBV inhibitors reduced NL activity in a dose‐dependent manner. Detection of HBV/NL infection, monitored by NL activity, was highly sensitive and less expensive than detection using the conventional method to evaluate HBV infection. In addition, because we also studied host factors, this system is applicable not only for studying the HBV life cycle, but also for exploring agent(s) that regulate HBV proliferation.  相似文献   
996.
997.
998.
999.
1000.
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